Piezoelectric and Magnetoelectric Thick Films for Fabricating Power Sources in Wireless Sensor Nodes

Transcription

1 Sensos 009, 9, ; doi: /s OPEN ACCESS sensos ISSN Review Piezoelectic and Magnetoelectic Thick Films fo Fabicating Powe Souces in Wieless Senso Nodes Shashank Piya 1, *, Jungho Ryu, Chee-Sung Pak 1, Josiah Olive 1, Jong-Jin Choi and Dong-Soo Pak 1 Cente fo Enegy Havesting Mateials and Systems CEHMS, Dept. of Mateials Science and Engineeing, Viginia Polytechnic Institute and State Univesity, Blacksbug, VA 4061, USA; s: pcs94@vt.edu C.-S.P.; joolive1@vt.edu J.O. Functional Ceamics Reseach Goup, Koea Institute of Mateials Science KIMS, Changwon, Gyeongnam , Koea; s: jhyu@kims.e.k J.R.; pds1590@kims.e.k D.-S.P. * Autho to whom coespondence should be addessed; 310 Duham Hall, Viginia Tech., Blacksbug, VA 4061; spiya@vt.edu; Tel.: ; Fax: Received: 3 July 009; in evised fom: 10 August 009 / Accepted: 11 August 009 / Published: 17 August 009 Abstact: In this manuscipt, we eview the pogess made in the synthesis of thick filmbased piezoelectic and magnetoelectic stuctues fo havesting enegy fom mechanical vibations and magnetic field. Piezoelectic compositions in the system PbZ,TiO 3 PbZn 1/3 Nb /3 O 3 PZNT have shown pomise fo poviding enhanced efficiency due to highe enegy density and thus fom the base of tansduces designed fo captuing the mechanical enegy. aminate stuctues of PZNT with magnetostictive feite mateials povide lage magnitudes of magnetoelectic coupling and ae being tageted to captue the stay magnetic field enegy. We analyze the models used to pedict the pefomance of the enegy havestes and pesent a full system desciption. Keywods: piezoelectic; magnetoelectic; enegy havesting; thick films; MEMS

2 Sensos 009, Intoduction Wieless senso nodes ae used in a wide spectum of applications, anging fom the human body to the oceans to industial machines. One can envision a pesonal health monitoing system whee extenal senso nodes measue the body tempeatue, pulse ate, and blood pessue and tansmit the data to a PDA o anothe hand held wieless devices. Senso nodes can also be implanted in the human body to monito glucose levels and toxins, while communicating with outside contol devices. In the ocean envionment thee ae a vaiety of deployable wieless senso netwoks that conduct opeations such as suveillance, chemical and biological studies, and oil exploation. In case of industial applications, a vaiety of sensos ae utilized to monito pocess and manufactuing opeations including, gas, chemical, tempeatue, stain, humidity, motion, stuctual health, and explosives. In all these applications the lifetime of the senso node is limited by the size of battey. In the case of implanted devices, the battey is inaccessible and thus othe methods fo poweing the senso nodes ae equied. The advancement in CMOS-technology, IC manufactuing, and netwoking techniques utilizing Bluetooth communication have significantly educed the total powe equiements of wieless senso nodes. The development of ulta-low-powe components has lead to powe equiements which ae extemely small micocontolles ~160 μa/mhz, senso ~10 μa, tansceive RS-3 ~3 ma, and tansceive RS-485 ~10 μa [1]. Recently, esults have been epoted on the development of wieless senso nodes equiing powe consumption of a few hunded micowatts. Such nodes will fom the futue of dense ad hoc-netwoks tansmitting data fom 1 to 10 metes. Fo communication ove 10 metes, the senso netwoks ae pojected to opeate in a multi-hop fashion, eplacing lage tansmission distances with multiple low powe low cost nodes [ 8]. In ode fo the nodes to be conveniently placed and used they should be as small as possible, which puts an uppe limit on thei lifetime. If an electonic device with a 1 cm 3 non-echageable lithium battey at a max enegy density of,880 J/cm 3 o 800 watt hou pe lite wee to consume on aveage 100 µw of powe, the device would last 333 days. A lifetime of appoximately one yea is not pactical [9]. Even though the nodes in the wieless netwok will be much smalle than the 1 cm 3 aea, the powe equiements will foce them to use a battey of much lage size, enhancing the system volume. Clealy, thee is an acute need fo the development of altenative powe souces [10,11]. The powe equiement fo commecially available tansceives such as Cossbow s Mica seies, Sentilla nodes and Dust Netwok nodes, vaies between mw in the active state and less than 10 mw in the sleep state. This powe is consumed by pocessos, adio, and sensos, depending upon factos such as tansmission and eceive ate. The powe consumed by pocessos can ange fom 0. nj/instuction to nj/instuction at 35 khz to 400 MHz. The powe consumed by adio lies in the ange of 150 nj/bit fo shot distances. The senso powe equiement depends upon the mechanism utilized such as magnetic, piezoelectic, capacitive, etc. Piezoelectic and magnetoelectic sensos have the advantage that they ae passive and consume powe only fo pocessing and adio, thus futhe educing the enegy budget.

3 Sensos 009, In geneal, thee ae fou possible ways to addess the poblem of poweing the wieless senso nodes, as follows: 1 enhance the enegy density of stoage systems; educe the powe consumption of wieless nodes; 3 develop self-poweed nodes by geneating o scavenging powe and 4 develop othe novel methods fo poweing the nodes. Out of these vaious possible solutions the most efficient and pactical method is to develop self-poweed nodes by scavenging enegy fom the wasted ambient enegy. Table I shows the list of mechanical enegy souces available in vaious scenaios which can be tapped fo geneating electicity locally. Recently, ou focus has been on industial machines as the souce of enegy and also the platfom fo implementing wieless health monitoing senso netwok. In addition to vibations, industial machines ae also souce of stay magnetic fields which can be tapped fo geneating electicity using magnetoelectics. Thus, the same device can convet both mechanical and magnetic enegy into electicity. Table 1. Souces of enegy available in the suounding which ae/can be tapped fo geneating electicity [identified in fist daft of standads on vibation enegy havesting, Cente fo Enegy Havesting Mateials and Systems CEHMS]. Human body Vehicles Stuctues Industial Envionment Beathing, blood pessue, exhalation, body heat, walking, am motion, finge motion, jogging, swimming, eating, talking Aicaft, UAV, helicopte, automobiles, tains, ties, tacks, peddles, bakes, shock absobes, tubines Bidges, oads, tunnels, fam house stuctues, contol-switch, HVAC systems, ducts, cleanes, etc. Motos, compessos, chilles, pumps, fans, conveyos, cutting and dicing, vibating mach. Wind, ocean cuents, acoustic waves. Seveal commecial enegy havesting pototypes addessing the needs in industies anging fom housing to aicaft to industial pocess monitoing systems have been demonstated. Figue 1 shows some of the pototypes that have been deployed on vaious platfoms. Figue 1a shows the pictue of enocean Pushbutton Tansmitte Module PTM 00 which has been implemented in wall-mounted electical switches as shown in Figue 1c. The tansmitte geneates powe using the enegy haveste simila to one shown in Figue 1b ECO 100 which convets linea motion into electicity using an electomagnetic induction mechanism. The dimensions of haveste ae mm 3 and it can povide output pulse of up to 5 V fom a foce of 5 N with tavel distance of mm. Figue 1c shows the pictue of a wall switch whee devices like ECO 100 can find application. Figue 1d shows the pictue of Viginia Tech s pen which was found to geneate powe of 3 mw at 5 Hz and 1 mw at 3.5 Hz opeating unde displacement amplitude of 16 mm coesponding to an acceleation of appoximately 1.14 g ms at 5 Hz and 0.56 g ms at 3.5 Hz espectively [1]. The pen utilizes Faaday s law of electomagnetic induction whee a magnet oscillates inside a wound coil as shown in Figue 1e. The integated pen haveste pototype was found to geneate continuous powe of mw unde nomal human actions such as jogging and jumping, as shown in Figue 1f. Figue 1g,h shows photogaphs of vibation enegy havesting heat stess nodes developed by MicoStain Inc. fo

4 Sensos 009, Navy applications. The module consists of miniatue elative humidity RH senso, a dy bulb tempeatue senso and black body tempeatue senso that combined povide data fo detemining each ship compatments wet bulb globe tempeatue WBGT and heat stess indexes. The vibation haveste was attached to an ai compesso and tuned to wok at 5 Hz sinusoidal vibation of amplitudes millig s which was the pedominant vibation fequency of machine. Figue 1i shows the pictue of ship just to give an idea of woking platfom in tems of dimensions. Figue 1j k shows pictue of a tie pessue monitoing system TPMS developed by ASTRI [13,14]. Figue 1l shows the TPMS application platfom whee tie vibations ae being used to monito pessue and tansmit the data wielessly. All these esults shown in Figue 1 clealy demonstate the pomise of vibation enegy havesting technologies. Figue 1. Demonstated vibation enegy havesting systems. a c enocean Pushbutton Tansmitte Module PTM 00, ECO 100 haveste, and wall mounted switch Website: d f Viginia Tech s pen and integated pen haveste pototype geneating continuous powe of mw unde nomal human actions; g i vibation enegy havesting heat stess nodes developed by MicoStain Inc. Website: fo Navy applications taken fom: Enegy Havesting Technologies, Ed. S. Piya and D. Inman and and j l tie pessue monitoing system TPMS developed by ASTRI fo automobiles Website: a b c f d e g h i

5 Sensos 009, Figue 1. Cont. j k l. Vibation Enegy Havesting Taditionally, a single degee of feedom SDOF vibating mass-sping-dampe base excitation system has been used to descibe the magnitude of enegy that can be havested fom a vibation souce as shown in Figue. The equation of motion fo the vibating system is given as: m x t c [ x t y T t] k[ x t y t] 0 1 whee stiffness of sping is k, total amount of damping electical and paasitic mechanical is c T, seismic mass is m, displacement of the base is given by y, and the displacement of seismic mass is given by x. Figue. Diagam of a sping-mass-dampe base excitation system. c T m k z x y Equation 1 can be eaanged in ode to deive a diffeential equation fo the elative motion, zt, as a function of the base acceleation: mz t ct z t kz t my t whee zt is the elative motion of seismic mass with espect to housing. Using Equation, it can be shown that the total powe dissipated in dampe unde sinusoidal focing is given as:

6 Sensos 009, m TY n P T 3 1 T n n whee ξ T is the total damping atio of the system. At esonance, the total powe in the system can be split into sum of mechanical powe dissipated and the electical powe geneated: 3 n m my m ey PT Pm Pe n 4 whee the electical powe geneated is equal to P e ω, the mechanical powe dissipated is given by P m ω, and ξ e and ξ m ae the electical and mechanical damping atios espectively of the haveste. The maximum powe which can be geneated by the electical powe takeoff system occus when the electical damping is equal to mechanical damping ξ e = ξ m. Theefoe the maximum electical powe which can be geneated is given as [10]: m e m e 3 my n e, max n 5 16 m P Equation 5 epesents the theoetical maximum amount of electical powe which can be dissipated in electical load. Depending upon the amplitude, fequency ange, opeating tempeatue ange, and lifetime, any of the five mechanisms, namely electomagnetic, piezoelectic, electostatic, magnetoelectic and electets, can be selected to convet available vibation enegy into electicity. In this manuscipt, we eview the developments made in the field of piezoelectic and magnetoelectic enegy havesting, mainly focusing on thick films. Mateials pefomance plays key ole in the design of haveste. Detailed analytical model fo piezoelectic enegy havesting using bimoph tansduce has been poposed by Olive and Piya. Figue 3 shows the block diagam fom of a solution to illustate the effect of mechanical system on electical output and the feedback tem with which the electical system affects the mechanical vibation of system. The vaiables H s, F s and Us ae aplace tansfoms of modal focing, modal displacement, and output voltage. Using the block diagam, a tansfe function fom input focing function to output voltage and displacement can be calculated. The tansfe function fom input base excitation foce to output cuent can be calculated as: G U t F t 6 1 GH whee G is the though path which epesents the geneation of cuent fom mechanical motion, and H is the feedback path which epesents the electical damping that system places on stuctue.

7 Sensos 009, Figue 3. Block diagam fo esponse aound th mode of the paallel a = 1 and seies a = connected piezoelectic bimoph. The output voltage and powe fo a seies a = and paallel a = 1 bimoph aound the th mode can be educed to the following equations [15]: t j p t b e Y j j a C R a M dx x M j t U avg R U t P whee Ф x is the mode shape of the th mode of cantileve beam, is the length of beam, M t is the seismic mass, M b is mass of beam, U is the voltage acoss the load esistance and P avg is the powe. The modal mechanical focing tem is given as: 0 dt t y d M dx x dt t y d M t f t b 8 The modal coupling tem tansducing modal velocity to cuent in the electical equation is given as [15]: x E pc E pc dx x d s b h d dx dx x d s b h d whee h pc is the distance fom the ceamic centeline to the neutal axis. The backwad modal coupling ceating the electical damping on mechanical stuctue is given as: x s p s p E x dx x d h h h ah b d s dx x d whee h s and h p ae the thicknesses of the piezoceamic and substuctue layes, E s 11 is the modulus of elasticity fo the ceamic, d 31 is the piezoelectic constant, b is the width of the beam, and a = 1 fo bimoph layes connected in paallel, a = fo bimoph layes connected in seies [15]. The capacitance of bimoph is given as:

8 Sensos 009, C p b 11 h p Using Equations 7 11, it can be shown that piezoelectic mateial with high d 31, and g 31, and low loss is equied fo bimoph tansduce. The loss in piezoelectic mateial is mainly elated to dielectic and electomechanical losses. These paametes contibute to the electical damping. Dong et al. have pesented the equivalent cicuit model fo magnetoelectic enegy haveste as shown in Figue 4. Based upon this model, the induced voltage V induced acoss the dielectic laye unde open cicuit condition can be given as [16]: V induced Z c p F mh Z 1 m whee φ p is the electomechanical coupling facto, φ m is the magneto-elastic coupling facto, Z C is the capacitance impedance Z c = 1/jωpC 0 and Z m is the mechanical impedance. The negative - sign indicates the evesal of phase between the applied F o H and the induced voltage V induced. It can be seen fom Equation 1 that a high electomagnetic coupling and magneto-elastic coupling is equied to havest the vibation and magnetic field simultaneously. Figue 4. Equivalent cicuit model fo magnetoelectic enegy havesting. u I pc 0 II I p F Z m pc 0 H 3 φ m H 3 φ p :1 3. Piezoelectic Thick Films fo Enegy Havesting Figue 5 highlights the application spectum of piezoelectic thin/thick films. Piezoelectic thick films with thickness ange of m have been used in devices such as mico-fluidics, micopumps, acceleometes, and enegy havestes. In addition to enegy havestes, othe micoelectomechanical systems MEMS such as acceleometes, acoustic sensos, and infaed detectos also equie dense, cack-fee piezoelectic thick films [17 5]. Howeve, synthesis of thick films is complex, as it is moe susceptible to cacks by themal stesses induced by diffeence in themal expansion coefficients between the film and substate [6,7]. Anothe impotant paamete fo enhancement of feoelectic and piezoelectic popeties of films is textue. It is well known that electomechanical popeties of PbZ,TiO 3 PZT film stongly depends on cystallogaphic oientation [8 30]. Piezoelectic

9 Sensos 009, popeties of 001 oiented hombohedal PZT films nea mophotopic phase bounday MPB ae supeio than those of 111 oiented films ove the entie composition ange [31 35]. Figue 5. Application aeas of piezoelectic mateials with vaying thickness. In ode to fabicate high quality thin/thick PZT films, chemical o physical deposition methods such as sputteing, pulsed lase deposition PD, metal oganic chemical deposition MOCVD, solgel, tape casting, and sceen pinting have been employed [36 39]. Published techniques fo synthesis of PZT thin films can be divided into two categoies, those that use in-situ cystallization i.e., cystallization duing deposition and those that involve post-deposition cystallization. MOCVD and physical deposition at elevated tempeatues fall into the fome categoy [36]. Fo in-situ cystallization, oxygen patial pessue is known to be a citical pocess contol paamete. The second categoy includes most chemical and low tempeatue physical deposition techniques [37 39]. Peand post-cystallization pocesses ae also known to influence the nucleation, micostuctue, textue, and electical popeties of PZT films. Synthesis of cack-fee thick films by using PD, sputteing, and sol-gel equies caeful optimization of vaious synthesis paametes [40 43]. Pak et al. have epoted 100-oiented 8 m cack-fee thick film using sol-gel oute, as shown in Figue 6 [41]. By contolling the pyolysis steps, they wee able to obtain pefeed oientation and by using an oganic additive [polyvinylpyolidone PVP] they wee able to incease the thickness of film. Using the combination of these two paametes, 8-m-thick films with 111 o 100 textue wee successfully synthesized. A combinatoy pocess of sputteing and sol-gel with contolled nucleation and gowth has been used to synthesize 5 m thick 100-oiented high quality films exhibiting longitudinal piezoelectic coefficient of >300 pc/n [4,43]. The micostuctue and oientation of films was adjusted by fist synthesizing a thin seed laye deived fom sol-gel method, and then subsequent depositions by sputteing. The seed laye had the same composition as othe PZT layes. Initially, when a sputteed

10 Sensos 009, thin laye was deposited on seed laye, the film had small gains with columna stuctue; howeve, as the deposited film became thicke, it developed a lage non-columna gain stuctue with lateal gowth, as shown in Figue 7a,b. The size of gains nea the suface was lage than that nea the substate, indicating that gain bounday pinning effect becomes smalle as the distance fom seed laye inceases. Based on this obsevation, a multi-sputteing pocess was developed [43]. Figue 6. Coss-sectional image of 8 μm-thick 100 oiented PZT film using sol-gel [41]. Figue 7. Sputteing method with seed laye to contol the gain gowth. a schematic diagams of nomal sputteing on a seed laye, b coss-sectional view of 3.5 μm-thick film using nomal sputteing on a seed laye [4], c schematic of multi-sputteing on a seed laye, and d coss-sectional view of 5 μm-thick film using multi-sputteing on a seed laye [43]. By educing the thickness of film in each deposition step, its columna micostuctue was maintained, as shown in Figue 7c,d. Simultaneous optimization of both seed laye and multi-step sputteing pocess allowed suppessing the cack geneation pocess. It was found that when the film

11 Sensos 009, had small in-plane gain size and fibous columna stuctue, the cack geneation pocess was suppessed due to incease in stength and stuctual stability. Consequently, thickness of PZT film with 100 oientation was makedly inceased up to 5 μm which also inceased the piezoelectic popeties [43]. Piezoelectic popeties wee found to impove as the film thickness was inceased [41 43]. This phenomenon is mainly elated to eduction in clamping and damping effects of substate [44 47]. Substate clamping esticts the domain motion unde applied electic field. Howeve, it is difficult to diectly associate the change in piezoelectic popeties with degee of clamping in films, because these popeties also depend of othe micostuctual vaiables such as gain size, gain shape, poosity, and textue [41,44 47]. The degee of clamping is often appoximated by measuing the esidual stess in films [41,47]. Substate clamping can be educed if the films ae in fee-standing state [48]. Recently, we have demonstated systematic change in piezoelectic popeties by synthesizing and measuing popeties of thee sepaate stuctues, clamped, island, and fee-standing, as shown in Figue 8 [48]. The esults showed that both lateal clamping as well as substate clamping play an impotant ole in contolling the feoelectic esponse. Figue 8. Schematic diagam illustating two diffeent types of clamping in fully-clamped, island, and feestanding films [48]. Akedo et al. have intoduced aeosol-deposition AD technique fo synthesizing thick films [49,50]. This technique can povide cack-fee dense thin and thick films with thicknesses anging fom submicomete to seveal hunded micomete with vey fast deposition ates. Figue 9 shows a schematic diagam of an AD system, which consists of a caie gas supply system with mass flow contol, powde chambe containing the ceamic powde, and deposition chambe with motoed X Y stage and nozzle evacuated by otay vacuum pump with mechanical booste. These thee pats ae all connected by a tube. The aeosol chambe contains the stating powdes, which ae mixed with a caie gas to fom an aeosol. The deposition chambe is devised fo film fomation. This chambe is connected with a vacuum system including a otay vacuum pump and a mechanical booste pump. Duing deposition, the deposition chambe is evacuated by the vacuum system, and theefoe a pessue diffeence between the aeosol chambe and deposition chambe is poduced. The aeosolized

12 Sensos 009, ceamic paticles fom the aeosol chambe ae deliveed to the deposition chambe by caie gas due to the pessue diffeential between the two chambes. The paticles ae acceleated and ejected though a slit-type nozzle, impacted onto a substate to fom a dense film in the deposition chambe. Paticle velocity can be contolled by the caie gas flow ate. The desied film thickness and deposition aea can be obtained by scanning the substate on motoized X-Y-Z stage. Fine pattening fo the film is also possible by inseting a mask between the nozzle and the substate. AD is called as oom tempeatue impact consolidation RTIC because dense films ae fomed by collision of fine paticles with substate at oom tempeatue. Howeve, actual deposition mechanism has not yet been established [49,50]. Consideing pevious studies on AD, it can be simply pesumed that duing collision with substate, paticles ae boken into smalle pieces, ebound and impact each othe, and then fom the continuous film [49,50]. Consequently, the deposition of paticles by AD appeas to be lagely dependent on kinetic enegy and factue enegy of the pimay paticle, and theefoe paticle diamete and mechanical popeties of paticle such as stength ae consideed as impotant factos in poducing dense high-quality AD film [49]. Figue 9. Schematic diagam of an aeosol deposition AD system. Pak et al. have implemented this technique on vaious mateial systems including PZT-based compositions and ealized highly dense and well-cystallized piezoelectic thick films of up to 100 m thickness as shown in Figue 10 [51 54]. In tems of deposition aea, PZT films up to mm can be fabicated by AD with a 150 mm nozzle, as shown in Figue 11. Recently, mm TiO photocatalytic thin films have been deposited by AD, which indicate the futue possibility of fabicating PZT films on 1 wafes. AD-piezoelectic thick films exhibit excellent piezoelectic popeties due to high density and minimized substate clamping. AD pocess can also be used to induce dopants into the film in ode to tailo the specific popeties. Fo example, Zhang et al. [55] have epoted that Mn doping in PZT thin films inceases hysteetic popeties and educes fatigue. Recently, we have demonstated had piezoelectic PZT-PZN-Mn thick films ~10 m by AD technique [56] which opens possibilities to design high enegy density compositions.

13 Sensos 009, Figue 10. Coss-sectional view of piezoelectic film with vaious thickness by AD; a 3 μm, b 10 μm, c 0 μm, and d 100 μm [54]. Figue 11. age aea piezoelectic 10 m-thick films by AD. a mm on stainless steel and b on mm glass Piezoelectic Mico-Geneatos fo Wieless Senso Nodes Piezoelectic mico-geneatos have highe enegy density compaed to othe mechanisms such as electostatic, and electomagnetic ones [57 59]. PZT films have been widely used fo fabicating havestes because of thei supeio effective piezoelectic constant [4,5,60 63]. Jeon et al.

14 Sensos 009, demonstated a d 33 mode powe geneating device with intedigitated electodes that can delive 1.0 W fom 10.8g vibation amplitude at esonant fequency of 13.9 khz [4]. Howeve in most cases, the vibations available fo havesting enegy lie in the low fequency ange of Hz [58,59]. Fang et al. [60] have demonstated a MEMS-based PZT cantileve stuctue with Ni poof mass that was found to geneate.16 W powe fom 1g vibation at the esonance fequency of 609 Hz. Shen et al. [5] have studied a d 31 mode haveste with embedded Si poof mass which was found to geneate.15 W powe fom g vibation at esonance fequency of Hz. iu et al. [61] have epoted mico-geneatos using vaying length of beams in ode to ealize boadband behavio. The pototype was found to geneate 3.98 W powe fom 0.5 g vibation in the fequency ange of 6 to 34 Hz. Renaud et al. [6] have epoted a PZT based MEMS haveste with maximum powe of 40 W at 1.8 khz. Impotant chaacteistics of epoted MEMS based piezoelectic havestes ae summaized in Table. Figue 1. Plane Views of cantileves: a d 33 type and bd 31 type. Table. Chaacteistics of epoted piezoelectic mico-geneatos Powe Fequency Acceleation Powe density W Hz g W/cm 3 Mode Mateials Ref k ,037* d 33 PZT [4] ,843* d 31 PZT [60] ,7 d 31 PZT [5] d 31 PZT [61] k 1.9* 1,680* d 31 PZT [6] , d 31 AIN [63] * Estimated values Thee ae two piezoelectic modes d 31 and d 33 commonly used fo MEMS based piezoelectic tansduces as shown in Figue 1a,b. Figue 13 shows the coss-sectional views of these piezoelectic modes [4,64] and Equations 13 and 14 ae the epesentative elationship between stess XX o stain x 3 and electic field E i o voltage V 3i.

15 Sensos 009, x d3ie i 3 13 V3i xxg3i 14 whee x 3 is stain, V 3i is the open cicuit voltage, d 3i V/m and g 3i Vm/N ae piezoelectic constants, and i is the distance between electodes which could be eithe thickness of piezoelectic t piezo o. The geneated open-cicuit voltage of a d 33 type device will be much highe than that of the d 31 type geneato of simila beam dimensions. Figue 13. Two modes of piezoelectic convesion fom input mechanical stess. i Since the mass of a MEMS scale device is small, the opeating fequency anges ae quite high, in the ange of ~khz. In ode to ovecome this poblem, the natual tendency has been to incease the tip mass of the cantileve [5,60,61]. Howeve, this affects the mechanical integity and lifetime of haveste. Choi et al. [65] have ecently poposed vaious possible designs such as spial to educe the opeating fequency ange. This is an impotant aea of eseach in MEMS haveste in ode to expand the applicability in common scenaios. 4. Magnetoelectic Composites: Thick and Thin Film Magnetoelectic ME effect can be descibed as an induced electic polaization in a mateial when a magnetic field is applied to it, o an induced magnetization in a mateial when an electic field is applied to it [66 69]. ME effect can be descibed as the poduct popety of piezoelectic and piezomagnetic effects [70], o as the poduct popety of pyoelectic and pyomagnetic effects [71]. Most of the feomagnetic mateials show magnetostictive effect, howeve, piezomagnetic effect in these mateials has not been obseved. This implies that the stain caused by magnetic field in these mateials is not linealy popotional to the field stength but to the squae of magnetic field stength. Fo enegy havesting applications, ME composite stuctues can be used to enhance the geneated powe fom the mico-geneato. The ME poduct popety can be exploited to geneate electicity fom unused magnetic fields aound electic motos and additionally fom thei mechanical vibations. ME composites can also be used to convet the vibation enegy into electicity with highe efficiency.

16 Sensos 009, In a simple design, the vibations can be used to otate a mechanical assembly which consists of magnets theeby ceating the oscillating magnetic field [7]. Feo Solutions has demonstated a device based on this appoach which was able to povide an enegy density of.0 mw/cm 3 at 1 Hz and 100 mg. Thee has been significant advances in impoving the magnitude of ME coefficient of laminates which makes this technique pomising. A combined magnetic and vibation enegy havesting device may be implemented on silicon using the thin film deposition methods and fabication pocess flow descibed ealie and combining with mico-machining technique. Figue 14. Repoted ME composite film stuctues: 3-1 [73,74], 3-0 [76], and - [79]. 3-0 film 3-1 film - film Recently, multifeoic nanocomposite thin films of feoelectic and magnetostictive mateials have been epoted motivated by the wok of Zheng et al. [73 75], via physical deposition methods such as pulsed lase deposition PD and chemical solution methods such as sol-gel spin coating. Fom micostuctual point of view thee ae thee kinds of nanostuctued composite films, i.e., i 3-0 stuctues with magnetic spinel nanopaticles embedded in the feoelectic films [76,77], ii 1-3 heteostuctues vetical heteostuctues consisting of magnetic spinel pillas vetically embedded into feoelectic films [73,75], and iii - heteostuctues hoizontal nanostuctues consisting of altenating layes of feoelectic peovskite and magnetic oxide [78,79], as shown in Figue 1. Wan et al. [76] synthesized PZT-CoFe O 4 CFO composite thin film using sol-gel pocess and spincoating technique. The films exhibited both good magnetic and feoelectic popeties, and the ME

17 Sensos 009, effect of these films was found to be stongly dependent on magnetic bias and magnetic field fequency. Zheng et al. [73 75] epoted composite films whee aays of magnetic CFO nanopillas with diametes of 0 30 nm wee embedded in a feoelectic BTO matix. Othe combinations of PbTiO3 CoFe O 4 and BiFeO 3 CoFe O 4 have also been gown on STiO 3 single cystal substates. These composite films have been found to exhibit excellent feoelectic and feomagnetic popeties but thee is no ME coupling. It seems that these stuctues have significant leakage which esticts the poling pocess. On the othe hand, 3-0 and - heteostuctues have been found to exhibit finite ME coupling due to the fact that leakage poblem of magnetic phase can be avoided by contolling the volume faction. Recently, we have successfully implemented AD pocess to fabicate ME composite thick films [80]. A highly dense 3- nanocomposite ME thick films of PZT-PZN and Ni,Cu,ZnFe O 4 NCZF with thickness of ove 10 m was synthesized on platinized silicon substate at RT. The schematic and TEM micostuctue is shown in Figues 15a-b. The fabicated nanocomposite film showed well dispesed laminated magnetic NCZF platelets inside PZT-PZN piezoelectic matix. This stuctue eliminated the leakage poblems found in 1-3 ME composite films and minimized substate clamping effect, thus esulting in impoved ME coefficient of 150 mv/cm Oe as shown in Figue 15c. In addition to ME chaacteistics, the deposition ate of ME films was exceptionally highe ove 1 m/min than othe conventional thin film pocess. Figue 15. a schematics and b TEM micostuctue of PZNT-NCZF 3- ME composite film by AD. c ME coefficient of 3- ME composite film with PZNT-NCZF fabicated by AD as a function of DC magnetic bias field [80]. b a c

18 Sensos 009, Conclusions We pesented the eview on pototype commecial vibation enegy havestes and thei suitability fo wieless senso netwoks. A bief discussion was pesented on modeling of vibation enegy havestes. Using the analytical models, it was shown that piezoelectic mateial with high d 31 and g 31, with low loss is equied fo bimoph tansduce while high electomagnetic coupling and magnetoelastic coupling is equied to havest the vibation and magnetic field simultaneously using magnetoelectic composites. An in-depth discussion was povided on synthesis of thick films using AD. This is an extemely impotant development as lage aea deposition capability with excellent film quality will allow tansitioning the mico-scale pototype devices. Combining the developments in the aea of piezoelectic thick films with mico-machining techniques will allow fabication of costeffective enegy havestes. Acknowledgements This wok was financially suppoted by Amy Reseach Office, Patt & Whitney and Ai Foce Office of Scientific Reseach. The authos fom KIMS acknowledge the funding though Component- Mateial development pogamme, Ministy of Knowledge Economy, Republic of Koea. Refeences 1. Muay, C.J. Enegy Havesting Gets Real. Design News. Octobe 008. Available at: accessed Mach 16, Rabaey, J.M.; Amme, M.J.; da Silva, J.., J.; Patel, D.; Roundy, S. PicoRadio Suppots ad Hoc Ulta-ow Powe Wieless Netwoking. Compute 000, 33, Gates, B. The disappeaing compute. In The Wold in 003; The Economist Goup: New Yok, NY, USA, Hitachi Unveils Smallest RFID Chip. RFID J. 003, Mach 14. Available at: accessed August 11, Douseki, T.; Shigematsu, S.; Tanabe, Y.; Haada, M.; Inokawa, H.; Tsuchiya, T.; A 0.5 V SIMOX- MTCMOS Cicuit with 00 ps ogic Gate. Solid-State Cicuits Confeence, Digest of Technical Papes. 4nd ISSCC., 1996 IEEE Intenational, San Fancisco, CA, USA, Febuay 1996; pp Jones, C.E.; Sivalingam, K.M.; Agawal, P.; Chen, J.C. A Suvey of Enegy Efficient Netwok Potocols fo Wieless Netwoks. Wiel. Netw. 001, 7, Roundy, S.; Wight, P.K.; Rabaey, J.M. Enegy Scavenging fo Wieless Senso Netwoks; Kluwe Academic Publishes: Boston, MA, USA, Octobe Calaway, E.H., J. Wieless Senso Netwoks; IEEE Pess: New Yok, NY, USA, Enegy Havesting Technologies, Piya, S., Inman, D.J., Eds.; Spinge Science+Business Media Inc.: Nowell, MA, USA, 008.

19 Sensos 009, Anton, S.R.; Sodano, H.A. A Review of Powe Havesting Using Piezoelectic Mateials Smat Mate. Stuct. 007, 16, R1 R Sodano, H.A.; Inman, D.J.; Pak, G.; A Review of Powe Havesting fom Vibation Using Piezoelectic Mateials. Shock Vibation Digest 004, 36, Bedeka, V.; Olive, J.; Piya, S. Pen Haveste fo Poweing a Pulse Rate Senso. J. Phys. D Appl. Phys. 009, 4, : : Cost-Effective Packaging Solutions fo Automotive Electonics. techpogam/mpt/mpt0_apt05.pdf accessed August 11, Sham, I. Into of ASTRI & Enegy Havesting Solutions fo Electonic Poducts. Pesentation at IDTechEx Enegy Havesting and Stoage Confeence, Cambidge, UK, June 3 4, Etuk, A.; Inman, D.J. An Expeimentally Validated Bimoph Cantileve Model fo Piezoelectic Enegy Havesting fom Cantileveed Beams. Smat Mate. Stuct. 008, 18, 05009: : Dong, S.; Zhai, J.; i, J.F.; Viehland, D.; Piya, S. Multimodal System fo Havesting Magnetic and Mechanical Enegy. Appl. Phys. ett. 008, 93, : : Scott, J.F.; Paz De Aaujo, C.A. Feoelectic Memoies. Science 1989, 46, Paz De Aaujo, C.A.; Cuchiao, J.D.; McMillan,.D.; Scott, M.C.; Scott, J.F.; Fatigue-Fee Feoelectic Capacitos with Platinum Electodes. Natue 1995, 374, Yamakawa, K.; Imai, K.; Aisumi, O.; Aikado, T.; Yoshioka, M.; Owada, T.; Okumua, K. Novel PbTi,ZO 3 PZT Cystallization Technique Using Flash amp fo Feoelectic RAM FeRAM Embedded SIs and One Tansisto Type FeRAM Devices. Jpn. J. Appl. Phys. 00, 41, Baik, S.; Sette, N.; Auciello, O. Peface: Science of Feoelectic Thin Films and Application to Devices. J. Appl. Phys. 006, 100, : :1. 1. Nam, H.-J.; Kim, Y.-S.; Cho, S.-M.; ee, C.S.; Bu, J.-U.; Hong, J.-W.; Khim, Z.-G. Calibation of Non inea Popeties of PbZ,TiO 3 Cantileve Using Integated Piezoesistive Senso fo High Speed Atomic Foce Micoscopy. Jpn. J. Appl. Phys. 00, 41, Polla, D..; Fancis,.F. Feoelectic Thin Films in Micoelectomechanical Systems Applications. MRS Bull. 1996, 1, Speaing, S.M. Mateials Issues in Micoelectomechanical Systems MEMS. Acta Mate. 000, 48, Jeon, Y.B.; Sood, R.; Jeong, J.-H; Kim, S.-G.; MEMS Powe Geneato with Tansvese Mode Thin Film PZT. Sens. Actuat. A 005, 1, Shen, D.; Pak, J.-H.; Ajitasia, J.; Choe, S.-Y.; Wikle III, H.C.; Kim, D.-J. The Design, Fabication and Evaluation of a MEMS PZT Cantileve with an Integated Si Poof Mass fo Vibation Enegy Havesting. J. Micomech. Micoeng. 008, 18, : :7. 6. Evans, A.G.; Hutchison, J.W. The Themomechanical Integity of Thin Films and Multilayes. Acta Metall. Mate. 1995, 43, Zhou, Y.C.; Yang, Z.Y.; Zheng, X.J. Residual Stess in PZT Thin Films Pepaed by Pulsed ase Deposition. Suf. Coat. Tech. 003, 16, Pak, S.-E.; Shout, T.R.; Ultahigh Stain and Piezoelectic Behavio in Relaxo Based Feoelectic Single Cystals. J. Appl. Phys. 1997, 8,

20 Sensos 009, Du, X.; Belegundu, U.; Uchino, K. Cystal Oientation Dependence of Piezoelectic Popeties in ead Ziconate Titanate: Theoetical Expectation fo Thin Films. Jpn. J. Appl. Phys. 1997, 36, Du, X.; Zheng, J.; Belegundu, U.; Uchino, K. Cystal Oientation Dependence of Piezoelectic Popeties of ead Ziconate Titanate Nea the Mophotopic Phase Bounday. Appl. Phys. ett. 1998, 7, Kalpat, S.; Du, X.; Abothu, I.R.; Akiba, A.; Goto, H.; Uchino, K. Effect of Cystal Oientation on Dielectic Popeties of ead Ziconium Titanate Thin Films Pepaed by Reactive RF-Sputteing. Jpn. J. Appl. Phys. 001, 40, Chen, S.-Y.; Chen, I.-W. Tempeatue-Time Textue Tansition of PbZ 1-x Ti x O 3 Thin Films: I, Role of Pb-ich Intemediate Phase. J. Am. Ceam. Soc. 1994, 77, Chen, S.-Y.; Chen, I.-W. Tempeatue-Time Textue Tansition of PbZ 1-x Ti x O 3 Thin Films: II, Heat Teatment and Compositional Effects. J. Am. Ceam. Soc. 1994, 77, Chen, S.Y.; Sun, C.. Feoelectic Chaacteistics of Oiented PbZ 1-x Ti x O 3 films. J. Appl. Phys. 001, 90, Taylo, D.V.; Damjanovic, D. Piezoelectic Popeties of Rhombohedal PbZ,TiO 3 Thin Films with 100, 111, and Random Cystallogaphic Oientation. Appl. Phys. ett. 000, 76, Shimizu, M.; Okaniwa, M.; Fujisawa, H.; Niu, H. Cystalline and Feoelectic Popeties of PbZ,TiO 3 Thin Films Gown by ow-tempeatue Metaloganic Chemical Vapo Deposition. Jpn. J. Appl. Phys. 00, 41, Books, K.G.; Reaney, I.M.; Klissuska, R.; Huang, Y.; Busill,.; Sette, N. Oientation of Rapid Themally Annealed ead Ziconate Titanate Thin Films on 111 Pt Substates. J. Mate. Res. 1994, 9, Kupanidhi, S.B.; Maffei, N.; Saye, M.; El-Assal, K. Rf Plana Magneton Sputteing and Chaacteization of Feoelectic PbZ,TiO 3 Films. J. Appl. Phys. 1983, 54, Hau, S.K.; Wong, K.H.; Chan, P.W.; Choi, C.. Intinsic Resputteing in Pulsed-ase Deposition of ead-ziconate-titanate Thin Films. Appl. Phys. ett. 1995, 66, Wang, Z.J.; Kikuchi, K.; Maeda, R. Effect of Pb contents in Taget on Electical Popeties of ase Ablation Deived ead Ziconate Titanate Thin Films. Jpn. J. Appl. Phys. 000, 39, Pak, G.-T.; Pak, C.-S.; Choi, J.-J.; ee, J.-W.; Kim, H.-E. Effects of Thickness on Piezoelectic Popeties of Highly Oiented ead Ziconate Titanate Films. J. Am. Ceam. Soc. 006, 89, Pak, C.-S.; ee, J.-W.; Pak, G.-T.; Kim, H.-E.; Choi, J.-J. Micostuctual Evolution and Piezoelectic Popeties of Thick PZT Films Deposited by Multi-Sputteing: Pat I. Micostuctual Evolution. J. Mate. Res. 007,, Pak, C.-S.; ee, J.-W.; Pak, G.-T.; Kim, H.-E.; Choi, J.-J. Micostuctual Evolution and Piezoelectic Popeties of Thick PZT Films Deposited by Multi-Sputteing: Pat II. Piezoelectic popeties. J. Mate. Res. 007,, Chen,.; i, J.-H.; Slutske, J.; Ouyang, J.; Roytbud, A.. Contibution of Substate to Convese Piezoelectic Response of Constained Thin Films. J. Mate. Res. 004, 19, Toah, R.N.; Beeby, S.P.; White, N.M. Expeimental Investigation into the Effect of Substate

21 Sensos 009, Clamping on the Piezoelectic Behavio of Thick-Film PZT Elements. J. Phys. D: Appl. Phys. 004, 37, Gwic, S.N.; Negeia, C.A. Evaluation of the Effect of Poosity and Substate on the Piezoelectic Behaviou of Thick-Film PZT Element. J. Phys. D: Appl. Phys. 006, 39, Sengupta, S.S.; Pak, S.M; Payne, D.A.; Allen,.H. Oigins and Evolution of Stess Development in Sol-Gel Deived Thin ayes and Multideposited Coatings of ead Titanate. J. Appl. Phys. 1998, 83, Ryu, J.; Piya, S.; Pak, C.-S.; Kim, K.-Y.; Choi, J.-J.; Hahn, B.-D.; Yoon, W.-H.; ee, B.-K.; Pak, D.-S.; Pak, C. Enhanced Domain Contibution to Feoelectic Popeties in Feestanding Thick Films. J. Appl. Phys. 009, 106, 04108: : ebedev M.; Akedo, J. Effect of Thickness on the Piezoelectic Popeties of ead Ziconate Titanate Films Fabicted by Aeosol Deposition Method. Jpn. J. Appl. Phys. 00, 41, Akedo, J. Aeosol Deposition of Ceamic Thick Films at Room Tempeatue: Densification Mechanism of Ceamic ayes. J. Am. Ceam. Soc. 006, 89, Choi, J.-J.; Jang, J.-H.; Han, B.-D.; Pak, D.-S.; Yoon, W.-H.; Ryu, J.; Pak, C. Pepaation of Highly dense PZN-PZT Thick Films by the Aeosol Deposition Method Using Excess-PbO Powde. J. Am. Ceam. Soc. 007, 90, Ryu, J.; Choi, J.-J.; Han, B.-D.; Pak, D.-S.; Yoon, W.-H.; Kim, K.-Y. Sinteing and Piezoelectic Popeties of KNN Ceamics Doped with KZT. IEEE Tans. Ultason. Feoelect. Equation Contol. 007, 54, Ryu, J.; Choi, J.-J.; Han, B.-D.; Pak, D.-S.; Yoon, W.-H.; Kim, K.-H. Fabication and Feoelectic Popeties of High Dense ead-fee Piezoelectic K 0.5 Na 0.5 NbO 3 thick Films by Aeosol Deposition. Appl. Phys. ett. 007, 90, Han, B.-D. Piezoelectic Thick Films. Ph.D Thesis, Seoul National Univesity, Seoul, Koea, Zhang, Q.; Whatmoe, R.R. Hysteetic Popeties of Mn-Doped PbZ,TiO 3 Thin Films. J. Euo. Ceam. Soc. 004, 4, Ryu, J.; Pak, C.-S.; Kim, K.-Y.; Choi, J.-J.; Pak, C.; Hahn, B.-D.; Yoon, W.-H.; ee, B.-K.; Pak, D.-S.; Piya, S. Had Piezoelectic PbZ 0.5 Ti 0.48 O 3 -PbZn 1/3 Nb /3 O 3 -MnO Thick Film by Aeosol-Deposition. Phil. Mag. Phil. ett. 009, in pess. 57. Williams, C.B.; Yates, R.B. Analysis of a Mico-Electic Geneato fo Micosystems. Sens. Actuat. A 1996, 5, Roundy, S.; Wight, P.K.; Rabaey, J. A Study of ow evel Vibations as a Powe Souce fo Wieless Senso Nodes. Comput. Commun. 003, 6, Piya, S. Advances in Enegy Havesting Using ow Pofile Piezoelectic Tansduces. J. Electoceam. 007, 19, Fang, H.-B.; iu, J.-Q.; Xu, Z.-Y.; Dong,.; Wang,.; Chen, D.; Cai, B.-C.; iu, Y. Fabication and Pefomance of MEMS-Based Piezoelectic Powe Geneato fo Vibation Enegy Havesting. Micoelecton. J. 006, 37,

22 Sensos 009, iu, J.-Q.; Fang, H.-B.; Xu, Z.-Y.; Mao, X.-H.; Shen, X.-C.; Chen, D.; iao, H.; Cai, B.-C. A MEMS-Based Piezoelectic Powe Geneato Aay fo Vibation Enegy Havesting. Micoelecton. J. 008, 39, Renaud, M.; Kaakya, K.; Steken, T.; Fioini, P.; Hoof, C.V.; Pues, R. Fabication, Modelling and Chaacteization of MEMS Piezoelectic Vibation Havestes. Sens. Actuat. A 008, , Mazencki, M.; Amma, Y.; Basou, S. Integated Powde Havesting System Including a MEMS Geneato and a Powe Management Cicuit. Sens. Actuat. A 008, , Xu, B.; Ye, Y.; Coss,.E.; Benstein, J.J.; Mille, R. Dielectic Hysteesis fom Tansvese Electic Fields in ead Ziconate Titanate Thin Films. Appl. Phys. ett. 1999, 74, Choi, W.J.; Jeon, Y.; Jeong, J.-H.; Sood, R.; Kim, S.G. Enegy Havesting MEMS Device Based on Thin Film Piezoelectic Cantileves. J. Electoceam. 006, 17, Cuie, P. Su la Symétie dans les Phénomènes Physiques. J. Phys. 1894, 3 ed Se., O Dell, T.H. Magnetoelectics- A New Class of Mateials. Electon. Powe 1965, 11, Ryu, J.; Caazo, A.V.; Uchino, K.; Kim, H.-E. Magnetoelectic Popeties in Piezoelectic and Magnetostictive amina Composites. Jpn. J. Appl. Phys. 001, 40, Ryu, J.; Piya, S.; Uchino, K.; Kim, H.-E. Magnetoelectic Effect in Composites of Magnetostictive and Piezoelectic Mateials. J. Electoceam. 00, 8, Suchetelene, J.V. Poduct Popeties: A New Application of Composite Mateials. Philips Res. Repot 197, 7, Newnham, R.E.; Skinne, D.P.; Coss,.E. Connectivity and Piezoelectic-Pyoelectic Composites. Mat. Res. Bull. 1978, 13, Kim, H.; ee, W.-H.; Dias, R.; Piya, S. Piezoelectic Micogeneato-Cuent Status, and Challenges. IEEE Tans. Ultason. Feoelect. FEquation Contol. 009, in pint. 73. Zheng, H.; Wang, J.; ofland, S.E.; Ma, Z.; Mohaddes-Adabili,.; Zhao, T.; Salamanca-Riba,.; Shinde, S.R.; Ogale, S.B.; Bai, F.; Viehland, D.; Jia, Y.; Schlom, D.G.; Wuttig, M.; Roytbud, A.; Ramesh, R. Multifeoic BaTiO 3 -CoFe O 4 Nanostuctues. Science 004, 303, Zheng, H.; Wang, J.; Mohaddes-Adabili,.; Wuttig, M.; Salamanca-Riba,.; Schlom, D.G.; Ramesh, R. Thee-Dimensional Hetetoepitaxy in Self-Assmbled BaTiO 3 -CoFe O 4 Nanostuctues. Appl. Phys. ett. 004, 85, Zavaliche, F.; Zheng, H.; Mohaddes-Adabili,.; Yang, S.Y.; Zhan, Q.; Shafe, P.; Reilly, E.; Chopdeka, R.; Jia, Y.; Wight, P.; Schlom, D.G.; Suzuki, Y.; Ramesh, R. Electic Field-Induced Magnetization Switching in Epitaxial Columna Nanostuctues. Nano ett. 005, 5, Wan, J.G.; Zhang, H.; Wang, X.; Pan, D.; iu, J.-M.; Wang, G.; Magnetoelectic CoFe O 4 -ead Ziconate Titanate Thick Films Pepaed by a Polyvinylpyolidone-Assisted Sol-Gel Method. Appl. Phys. ett. 006, 89, 1914:1 1914: Ryu, H.; Muugavel, P.; ee, J.H.; Chae, S.C.; Noh, T.W.; Oh, Y.S.; Kim, H. J.; Kim, K. H.; Bae, C.; Pak, J.-G. Magnetoelectic Effects of Nanopatiulate PbZ 0.5 Ti 0.48 O 3 -NiFe O 4 Composite Films. Appl. Phys. ett. 006, 89, 10907: :3.

23 Sensos 009, Zhou, J.-P.; He, H.; Shi, Z.; Nan, C.-W. Magnetoelectic CoFe O 4 /PbZ 0.5 Ti 0.48 O 3 Double-aye Thin Film Pepaed by Pulsed-ase Deposition. Appl. Phys. ett. 006, 88, : : Ma, Y.G.; Cheng, W.N.; Ning, M.; Ong, C.K. Magnetoelectic Effect in Epitaxial PbZ 0.5 Ti 0.48 O 3 /a 0.7 S 0.3 MnO 3 Composite Thin Film. Appl. Phys. ett. 007, 90, 15911: : Pak, C.-S.; Ryu, J.; Choi, J.-J.; Pak, D.-S.; Ahn, C.-W.; Piya, S; Giant Magnetoelectic Coefficient in 3- Nanocomposite Thick Films. Jpn. J. Appl. Phys. 009, 48, 08004: : by the authos; licensee Molecula Divesity Pesevation Intenational, Basel, Switzeland. This aticle is an open-access aticle distibuted unde the tems and conditions of the Ceative Commons Attibution license