pss Effects of O 2 plasma treatment on low temperature solution-processed zinc tin oxide thin film transistors solidi physica status

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1 Phy. Sttu Solidi A, 1 5 (2013) / DOI /p Effect of O 2 plm tretment on low temperture olution-proceed zinc tin oxide thin film trnitor Jeong-Soo Lee 1, Seung-Min Song 1, Yong-Hoon Kim 2, Jng-Yeon Kwon *,3, nd Min-Koo Hn 1 1 School of Electricl Engineering nd Computer Science, Seoul Ntionl Univerity, Seoul , Kore 2 Flexible Diply Reerch Center, Kore Electronic Technology Intitute, Seongnm, Gyeonggi , Kore 3 School of Integrted Technology, Yonei Univerity, Incheon , Kore phyic p ttu olidi ppliction nd mteril cience Received 23 November 2012, revied 11 Mrch 2013, ccepted 12 April 2013 Publihed online 8 My 2013 Keyword oxide, plm tretment, olution proceing, thin-film trnitor, zinc tin oxide * Correponding uthor: e-mil jngyeon@yonei.c.kr, Phone: þ , Fx: þ The electricl chrcteritic uch threhold voltge, turtion mobility, nd electricl relibility of low temperture (350 8C) olution-proceed zinc tin oxide (ZTO) thin film trnitor (TFT) were improved coniderbly by employing O 2 plm tretment. O 2 plm tretment w performed by plm her nd cue preferentil diocition of wek hlide-relted bonding uch Cl bonding by ion bombrdment. After O 2 plm tretment, the threhold voltge decreed from 25.0 to 10.7 V becue of n incree in electron concentrtion due to the reduction of Cl bonding nd imultneou compoition of O-relted bonding. The turtion mobility w increed from 0.09 to 0.58 cm 2 V 1 1 becue of the incree in electron concentrtion nd reduction of the hlide reidue uch Cl tom cting trp tte by employing O 2 plm tretment. Moreover, the electricl relibility uch threhold voltge hift w improved from 5.34 to 3.23 V for poitive gte bi-tre becue O 2 plm reduced the hlide reidue uch Cl tom cting trp tte. 1 Introduction Solution-proceed oxide thin film trnitor (TFT) with indium gllium zinc oxide (IGZO) nd zinc tin oxide (ZTO) hve ttrcted coniderble ttention for the driving element of ctive mtrix diply becue of high mobility, viible light trnprency, nd good uniformity [1 3]. Furthermore, olution-proce h uitbility for lrge re nd high throughput nd could be method for chieving low cot fbriction contrry to vcuum procee [4, 5]. Among vriou ZnO-bed oxide emiconductor, ZTO TFT employing Tin (Sn) mteril mybe promiing cndidte for chieving low cot procee becue Sn i quite low cot mteril compred with widely ued indium (In) [4]. Therefore, ZTO TFT employing Sn mybe promiing cndidte for chieving low cot procee. Solution-proceed ZTO TFT need to be fbricted on inexpenive nd flexible ubtrte uch gl nd pltic for dditionl cot reduction nd ppliction extenion to flexible diply. For olution-proceed ZTO TFT fbriction with thee flexible ubtrte, low temperture procee re necery becue thee ubtrte re eily dmged t high nneling temperture. At low nneling temperture, however, olution-proceed ZTO TFT hve poor performnce uch low on-current, high threhold voltge, nd low mobility, o rther high nneling temperture exceeding 500 8C i required in olution-proceed ZTO TFT [5, 6]. Therefore, the effort to chieve high device chrcteritic of olution-proceed ZTO TFT even t low nneling temperture on ctive lyer re deired. The purpoe of thi pper i to report tht the electricl chrcteritic uch threhold voltge, turtion mobility, nd relibility of olution-proceed ZTO TFT could be coniderbly improved by employing O 2 plm tretment even t n low nneling temperture of 350 8C nd to invetigte the effect of O 2 plm tretment on low temperture (350 8C) olution-proceed ZTO TFT. 2 Experimentl Solution-proceed ZTO TFT with inverted tggered tructure were fbricted on the ilicon wfer ubtrte hown in Fig. 1(). Hevily boron doped

2 phyic p ttu olidi 2 J.-S. Lee et l.: Effect of O 2 plm tretment on olution-proceed zinc tin oxide TFT 1E-5 RTA 350 C RTA 350 C O2 plm 100 W RTA 350 C O2 plm 300 W IDS [A] 1E-14 V GS [V] Soluble ZTO TFT V DS = 10 V Figure 2 Trnfer chrcteritic of olution-proceed ZTO TFT with n nneling temperture of 350 8C by employing O 2 plm tretment of 100 nd 300 W with W/L ¼ 100 mm/ 10 mm nd V DS ¼ 10 V. Figure 1 () Structure of inverted tggered olution-proceed ZTOTFTnd(b)cro-ectionlviewofZTOctivefilm,SiO 2 gte inultor, nd Si wfer ubtrte. p-type ilicon wfer ubtrte nd therml oxidized ilicon dioxide (SiO 2 ) were ued the gte nd gte inultor, repectively. The cro-ectionl view of ZTO ctive film, SiO 2 gte inultor, nd Si wfer ubtrte i hown Fig. 1(b) by trnmiion electron microcopy (TEM). The precuror-bed olution of ZTO for ctive lyer w prepred with zinc chloride (ZnCl 2 ) nd tin (II) chloride (SnCl 2 ) powder in cetonitrile (CH 3 CN) t equl molr rtio. The ZTO film w depoited by pin-coting nd iolted by the wet-etching proce uing diluted HF. And the ZTO film were nneled t 350 8C for 10 min by rpid therml nneling (RTA) proce. After the ZTO film were formed on the SiO 2,O 2 plm tretment w performed with flow rte of 30 ml min 1 nd plm power of 100 nd 300 W for 10 min on ZTO ctive lyer by plm her in order to improve the chrcteritic of olution-proceed ZTO TFT without ny ubtrte heting. Indium zinc oxide (IZO) film w depoited by dc puttering nd then defined by lift-off proce to yield ource nd drin electrode. Finlly, poly(methyl methcrylte) (PMMA) lyer w employed for pivtion to protect the ctive lyer from wter in the ir. 3 Reult nd dicuion The drin current-gte voltge trnfer chrcteritic of 350 8C low temperture olution-proceed ZTO TFT with length (L)of 10 mm nd width (W) of 100 mm in the drk t room temperture re invetigted hown in Fig. 2. When O 2 plm power incree to 300 W, the on-current were increed, while off-current re not vried coniderbly. Epecilly the threhold voltge decreed drticlly to the negtive direction with the incree in O 2 plm power. Thee re ummrized gin in Fig. 3 tht the threhold voltge of 350 8C low temperture olution-proceed ZTO TFT decreed grdully from 25 to V with the incree in O 2 plm power to 300 W. It h been lredy reported in recent report on putter-proceed oxide TFT tht the vrition of threhold voltge h been nlyzed by the chnge of electron concentrtion [7 9]. The decree in threhold voltge of olution-proceed ZTO TFT could be imilrly undertood being cued by the incree in electron concentrtion of the ZTO ctive lyer. Hll meurement reult confirmed tht when O 2 plm power incree to 300 W, the electron concentrtion of ZTO film increed from to , nd ccordingly, the threhold voltge decreed hown in Fig. 3 [10]. The incree in electron concentrtion of ZTO film due to O 2 plm could be explined by the decree in Cl tomic concentrtion [11]. O 2 plm tretment cue preferentil diocition of wek hlide-relted bonding uch Cl Figure 3 Threhold voltgendelectron concentrtion ofolutionproceed ZTO TFT with n nneling temperture of 350 8C ccording to O 2 plm power.

3 Originl Pper Phy. Sttu Solidi A (2013) 3 bonding nd imultneou compoition of O-relted bonding of ZTO film by ion bombrdment of energetic O 2 plm with promoting the rection of chemicl formtion Eq. (1) our previou work [12], ZnðOHÞCl þ SnðOHÞCl! ZnO SnO þ 2HClð"Þ: (1) Figure 4() nd (b) demontrte Auger electron pectrocopy (AES) reult of the chnge of Cl nd O tomic concentrtion, repectively, ccording to O 2 plm. In ZTO chnnel lyer region of Fig. 4() nd (b), Cl tomic concentrtion decreed grdully from 11.1 to 8.2% nd O tomic concentrtion rther increed from 51.7 to 53.8% t 100 Å depth of ZTO lyer, when O 2 plm power increed to 300 W. The decree in Cl tom nd incree in O tom cue tht Zn nd Sn tom would be bound to O tom when O 2 plm i pplied. Thee cue the decree in binding energy of ZTO film from OH Cl bonding to Zn O nd Sn O bonding with the incree in O 2 plm power [10]. Further, when binding energy decree, the oxygen vcncie generte electron more eily, nd conequently the electron concentrtion of ZTO ctive lyer incree [13 15]. In the interfce region with SiO 2 gte inultor of Figure 5 Cl tomic concentrtion nd turtion mobility of olution-proceed ZTO TFT with n nneling temperture of 350 8C ccording to O 2 plm power. Fig. 4() nd (b), Cl nd O tomic concentrtion were crcely ffected by O 2 plm tretment. H 2 plm tretment w lo performed on ZTO ctive lyer with plm power of 300 W. On the contrry to the effect of O 2 plm tretment, the tomic concentrtion of ZTO film with H 2 plm tretment were crcely ltered from tht of ZTO film without plm tretment. Ion bombrdment by plm tretment could be occurred effectively with O 2 tom thn H 2 tom becue O 2 h lrger moleculr weight thn tht of H 2. Therefore, O 2 plm tretment i uitble to improve the electricl chrcteritic of 350 8C low temperture olution-proceed ZTO TFT by ion bombrdment. The turtion mobility of 350 8C low temperture olution-proceed ZTO TFT w increed from 0.09 to 0.58 cm 2 V 1 1 when the O 2 plm power w increed to 300 W demontrted in Fig. 5. The incree in turtion Figure 4 Atomic concentrtion of ZTO film in AES nneled t 350 8C ccording to O 2 plm power for () Cl tom nd (b) O tom. Figure 6 ZTO ctive lyer with morphou phe regrdle of O 2 plm power with () XRD reult nd (b) TEM imge.

4 phyic p ttu olidi 4 J.-S. Lee et l.: Effect of O 2 plm tretment on olution-proceed zinc tin oxide TFT mobility could be cued by the crytlliztion nd/or the diocition of hlide reidue, but O 2 plm tretment did not cue the crytlliztion of ZTO ctive lyer with morphou phe regrdle of O 2 plm power hown in Fig. 6() nd (b), with X-ry diffrction (XRD) reult nd TEM imge repectively. () I DS [A] (b) IDS [A] (c) Threhold Voltge Shift [V] VGS [V] Soluble ZTO TFT RTA 350 ºC Stre (VGS = 10 V) time = 0 ec 10 ec 100 ec 1000 ec 3600 ec V GS [V] Soluble ZTO TFT RTA 350 ºC O2 plm 300 W Stre (VGS = 10 V) time = 0 ec 10 ec 100 ec 1000 ec 3600 ec Soluble ZTO 350 ºC Stre : VGS = 10 V & V DS = 0 V Without plm O 2 plm (300 W) Stre time [ec] Figure 7 Relibility chrcteritic of olution-proceed ZTO TFT with the poitive gte bi-tre of 10 V for 3600 () trnfer curve without O 2 plm tretment, (b) employing O 2 plm tretment of 300 W, nd (c) threhold voltge hift without O 2 plm tretment nd with O 2 plm tretment of 300 W. O 2 plm tretment cue the preferentil diocition of hlide reidue uch Cl bonding of ZTO film, reulting in the incree in electron concentrtion. The incree in electron concentrtion could incree the turtion mobility becue the hll mobility i proportionl to the crrier concentrtion in oxide emiconductor [16]. Moreover, the hlide reidue uch Cl tom in ZTO film re conidered trp tte cting obtcle for electron ccumultion nd trnporttion of electron in the conduction bnd, nd conequently reducing the mobility [10]. Therefore, the reduction of hlide reidue uch Cl tom with O 2 plm tretment, which i confirmed in AES reult of Fig. 4 bove, nd demontrted gin in Fig. 5, could incree the turtion mobility of olution-proceed ZTO TFT. The electricl relibility chrcteritic uch threhold voltge hift of 350 8C low temperture olution-proceed ZTO TFT were lo invetigted with the poitive gte bi-tre of 10 V for 3600 hown in Fig. 7. The threhold voltge of 350 8C low temperture olutionproceed ZTO TFT w hifted poitively by poitive gte bi-tre lmot without chnge of lope, regrdle of plm tretment. The threhold voltge hift for poitive gte bi-tre of olution-proceed ZTO TFT without plm tretment w 5.34 V Fig. 7(), but decreed to 3.23 V with n O 2 plm power of 300 W Fig. 7(b), o we could oberve the improvement in relibility by O 2 plm tretment demontrted in Fig. 7(c). It i nother upporting dt tht O 2 plm tretment reduce the hlide reidue uch Cl cting trp tte. 4 Concluion We fbricted low temperture olution-proceed ZTO TFT with n nneling temperture of 350 8C on ZTO ctive lyer which i coniderbly lower thn widely ued 500 8C nd employed O 2 plm tretment on ZTO ctive lyer to improve the electricl chrcteritic of olution-proceed ZTO TFT. O 2 plm tretment cue preferentil diocition of wek hlide-relted bonding uch Cl bonding by ion bombrdment. After O 2 plm tretment, the threhold voltge decreed from 25 to V with n O 2 plm power of 300 W becue of the incree in electron concentrtion from to due to the reduction of Cl bonding nd imultneou compoition of O-relted bonding by ion bombrdment. Moreover, the turtion mobility w increed from 0.09 to 0.58 cm 2 V 1 1 with n O 2 plm power of 300 W becue of the incree in electron concentrtion nd reduction of hlide reidue uch Cl tom trp tte. The electricl relibility chrcteritic uch threhold voltge hift of 350 8C low temperture olution-proceed ZTO TFT for poitive gte bi-tre w improved from 5.34 to 3.23 V with n O 2 plm power of 300 W becue O 2 plm reduced the hlide reidue uch Cl cting trp tte. Therefore, we hve uccefully improved the electricl chrcteritic of 350 8C low temperture olution-proceed ZTO TFT to decree threhold voltge nd enhnce

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