IMM Bologna. S3T Workshop, Porto, 6 th -9 th Apr. 2010

Transcription

1 MICRO ELECTRO MECHANICAL SYSTEMS FOR CRACK MONITORINGINAGEING IN INFRASTRUCTURES A. Roncaglia 1, M. Ferri 1, F. Mancarella 1, J. Yan 2, A. A. Seshia 2, K. Soga 2, J. Zalesky 3 1 CNR, Institute of Microelectronics and Microsystems (IMM), Bologna, Italy 2 University it of Cambridge, Engineering i Department, t Cambridge, UK 3 Technical University in Prague, Faculty of Civil Engineering, Prague, Czech Republic

2 Outline Underground M3 Project: Micro-Monitoring Monitoring and Measurement System for Ageing Underground Infrastructures Micro-Electro-Mechanical Systems (MEMS) in crack monitoring MEMS fabrication Packaging/Assembly g Prototyping of MEMS crackmeter and early tests 2

3 Computer vision S3T Project - Underground M3 Wireless sensor networks Project: Underground M3 Micro-measurement and monitoring system for ageing Underground Infrastructures, Eurocores S3T FP6 Start: Oct , End: Apr Coordinator: Prof. Kenichi Soga, University of Cambridge, UK Partners: University it of Cambridge (UK), CNR Institute t of Microelectronics and Microsystems (Italy), Technical University in Prague Advanced (Czech simulation Republic), methods Universidad Politecnica MEMS desensors Catalunya (Spain) Aim: Developing new methods for structural monitoring of underground infrastructures, particularly underground tunnels. 3

4 Underground M3: distributed sensors in tunnels 4

5 Objective: MEMS wireless crackmeter Possible design of MEMS-based wireless crackmeter Wall anchors PCB (wireless unit/sensor interface) Wall crack Silicon chip Steel bar Uniaxial strain sensors 5

6 Objective: MEMS wireless crackmeter Crack movement analysis through uniaxial strain detection on a triangular pattern 1. Expansion 2. Contraction 3. Sliding (A) 4. Sliding (B) 6

7 IMM Bologna S3T Workshop, Porto, 6th-9th Apr Micro--ElectroMicro Electro-Mechanical Mechanical--Systems y ((MEMS)) 1st Antisymmetric resonance mode 1st Symmetric resonance mode anchors suspended beam coupling gap actuation electrodes 7

8 Axial load MEMS resonators s as strain sensors so s Resonance frequency shift brated Amplitud de Spectrum [d db] Calibrated Amplitu ude Spectrum [db] Cali No No Strain) 72 strain Frequency [Khz] C 1 - C 2 MEMS Self-sustained oscillation at resonance Strain-dependent oscillator 8

9 Electromechanical properties p of resonant MEMS Motional current C I I m R m L m C m V dc Feedthrough current I ft C ft For closed loop operation must be I ft << I m R m = m α 2 eq 2 m eq f r α 2 L m = C m = Q α 2 α f 2 r m eq α = Ф 1 V dc ε 0 S d 2 9

10 The problem of packaging g Package MEMS [db] um [db] -50 Bonding wires ated Amplitude Spectrum [ Calibrated Amplitude Spectr Steel Frequency [Khz] [Khz] Electrical connections Vacuum packaging would be in principle the best solution MEMS resonator in air (800 Torr) MEMS resonator in vacuum (3 mtorr) 10

11 Objectives of MEMS activity within Undergound M3 Development of a MEMS fabrication technology for lateral l resonators with coupling gaps scaled below 1µm. Investigation of bonding techniques suited to fix the MEMS chip on steel with efficient strain transfer. Development of a vacuum packaging technique for MEMS strain sensors bonded on steel. Realization and test of afirst prototype of MEMS-based crackmeter. 11

12 MEMS sensors fabrication: process flow 1. SOI wafer 2. SiO 2 deposition 3. SiO 2 RIE etching Device layer: Si 15 µm Handle: Si 500 µm SiO2 2 µm 4. Polysilicon deposition 5. Oxidation 6. Oxide RIE etching 7. Scribeline etching 8. Device layer etching 9. HF vapour release 10. Metal deposition 12

13 IMM Bologna S3T Workshop, Porto, 6th-9th Apr MEMS fabrication: g gap p narrowing g tests 13

14 MEMS fabrication comb-drive DETF sensor so 14

15 MEMS fabrication parallel a plate pate DETF sensor so 15

16 MEMS fabrication: resonators with various geometries 16

17 MEMS fabrication: open-loop testing Open-loop measurements on parallel-plateplate DETF device: Vdc=20V, -25dBm, Signal peak >15dB, Q>20000, f0=490khz Devices with high Q and low feedthrough with grounded substrate: OK for closed-loop loop operation 17

18 Assembly: silicon/steel adhesive bonding Strain sensors: CEA UN-120 Vishay 11-FA RS Components Adhesives: M-Bond200, two-component cyanoacrylate y M-Bond600, two-component epoxy Experimental setup (2) Commercial strain gauge P Strain Gauge Adhesive (M-Bond200 /M-Bond600) Silicon die Adhesive (M-Bond200 /M-Bond600) Steel bar 18

19 Assembly: silicon/steel solder bonding Silicon sample Steel bar 1. Oxide etch 1. Oxide etch 4. Foil strain gauge sticking on silicon sample 2. Cu evaporation 2. Sn-Pb deposition 3. Pressure and heating (200 C) 19

20 Assembly: silicon/steel strain transfer ) Strain ( s L=40 mm t=4mm Strain Gauge Position 3/4 L Theoretical 100 N11-FA N11FA03120 CEA UN-120 CEA UN-120 on silicon (MBond 600). CEA UN-120 on silicon (MBond 200) Inflection (mm) Strain ( s s) L=41 mm t=2mm Strain Gauge Position 1/4 L Theoretical CEA UN-120 CEA UN-120 on silicon Inflection (mm) Adhesive bonding Solder bonding Strain transfer around 70 % Strain transfer above 90 % 20

21 Packaging: g vacuum packaging g by glass softening Vacuum packaging Prototype technique Measured vacuum level 10 0 Pres ssure (T Torr) Time (h) Best result with glass softening method: 300 mtorr Problems in reliability 21

22 Packaging: g vacuum packaging g by soldering Vacuum sealing with metal solder instead of glass softening 10-1 Pressure (Torr) Time (h) Results: improved reliability, improved vacuum level (40 mtorr) 22

23 Prototyping: crackmeter prototype with MEMS in vacuum 23

24 Prototyping: crackmeter prototype with MEMS in air MEMS sensor Piezoresistive sensor 24

25 Testing: crackmeter with MEMS in air Open loop measurements on Crackmeter prototype with MUMPS round disk resonators in air. The device shows some sensitivity to strain, but its electromechanical properties seem to be unsuitable for closed-loop loop operation (too large feedthrough and low peak, at least with capacitive sensing) 25

26 Testing: crackmeter with MEMS in vacuum Crackmeter prototype assembled with vacuum packaging of a parallel- plate DETF device MEMS sensor Piezoresistive sensor 26

27 Testing: crackmeter strain sensitivity Measurements on UCAM-CNR CNR parallel-plateplate resonator within the crackmeter with applied strain. 438,5 Calibra ated Amplitude Spectrum [d db] Nostrain 16ustrain 41ustrain 72ustrain 92ustrain 107ustrain 118ustrain Frequency [khz] Reson nance freq quency [kh Hz] 438,0 437,5 437,0 Strain loading Strain release 436, Strain [ s] Strain sensitivity of roughly 10 Hz/µStrain, stable results with constant applied strain, reversible operation. Strain applied in the range µstrain. 27

28 Conclusions A technology for the fabrication of lateral SOI MEMS resonators with good feedthrough immunity and Qup to 50, in vacuum has been developed. Strain transfer from steel to silicon has been evaluated to be around 70 % with adhesive bonding and above 90 %with solder bonding. Acrackmeter prototype has been assembled using a vacuum-packaged parallel-plateplate MEMS resonator and tested with a measurement setup. Open-loop testing of the crackmeter was successful, with resonator Qaround 9000 for Vac = V and peak height around 20 db. Strain sensitivity around 10 Hz/µStrain and measurement repeatability were also demonstrated using this prototype. Future developments Implementation of closed-looploop oscillation for the crackmeter with vacuum packaged MEMS. On-field testing of the crackmeter in Prague Underground. Implementation and testing of multi-directional strain sensing module on a new crackmeter prototype. 28