CMOS-MEMS Probes

…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....…...…...…...…...…...…...…......i Contents …....…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...iii Lists of Figures …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....ix Lists of Tables …......…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....xvii Acknowledgments …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....xviii 1 Introduction …...…...…...…...…...…...…...…...…...…...…....…...…...…...…...…...…...…...….......1 1. 1 Thesis Description and Contributions …...…...…...…...…...…...…...…...…...….....1 1. 2 Motivations …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....2 1. 2. 1 Reconfigurable Phase Change Materials …...…...…...…...…...…...…...…...…...…...2 1. 2. 2 MISCIC …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....6 1. 2. 3 Resistance Change Via Chip Fabrication …...…....…...…...…...…...…...….......10 1. 3 Prior Work …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......…...…......11 1. 3. 1 Probes with Force and/or Displacement Sensing …...…...…...…...…...….....11 1. 3. 2 High Current Contacts …...…...…...…...…...…...…...…...…...…...…...…...…...…......…......14 1. 3. 3 Electrothermal Actuation …...…...…...…...…...…...…...…...…......…...…...…...…...…......15 1. 4 Probe Specifications …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......16 1. 5 CMU CMOS-MEMS Process …...…...…...…...…...…...…...…...…...…...…...…...…...17 1. 6 Outline of Thesis …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….......21 ____________________________________________________CMOS-MEMS Probes iv 2 Electrothermal Actuation …...…...…...…...…...…...…...…...…...…...…...…...…...…....22 2. 1 Specifications and Objective …...…...…...…...…...…...…...…...…...…....…...…...…....22 2. 2 Working Theory for Electrothermal Actuation …...….....…...…...…...…...22 2. 3 History of Electrothermal Probes …...…...…...…...…...…...…...…....…...…...….....24 2. 4 Conceptual Mechanical Design and Analysis …...…...…...…...…...…...…...28 2. 4. 1 Metal-1 Flexures …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......28 2. 4. 1. 1 Stroke …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...28 2. 4. 1. 2 Self-Assembly …...…...…...…...…...…...…...…...…...…...…...…...…...…...…......34 2. 4. 2 Metal-3 Flexures …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......35 2. 4. 2. 1 Stroke …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...35 2. 4. 2. 2 Self-Assembly …...…...…...…...…...…...…...…...…...…...…...…...…...…...…......35 2. 4. 3 Spring Constant …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....37 2. 4. 4 ““Unwanted”” Lateral Actuation …......…...…...…...…...…...…...…...…...…...…...….....44 2. 4. 5 Summary of Five Generations of Probes …...…...…...…...…...…...…...…...….....45 2. 5 Thermal Management Design and Analysis …...…...…......…...…..........47 2. 5. 1 Dummy Heater Beams …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....47 2. 5. 2 Thermal Isolation Structures …...…...…...…...…...…...…...…...…...…...…...…...…...…....50 2. 5. 3 Thermal Cross-Talk …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....52 2. 6 Probe Characterization …...…...….....…...…...…...…...…...…...…...…...…...…...…...…....56 2. 6. 1 Spring Constant …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....59 2. 6. 2 Silicon Undercut …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......60 2. 6. 3 Self-Assembly Displacement …...…...…...…...…...…...…...…...…...…...…...…...…...…...61 ____________________________________________________CMOS-MEMS Probes v 2. 6. 4 Actuation …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....….....64 2. 6. 4. 1 Displacement versus Drive Power …...…...…...…....…...…...…...…....…...64 2. 6. 4. 2 Frequency Response …...…...…...…...…...…...…...…...…...…...…...…...…....….....64 2. 6. 4. 3 Dummy Heater Beams …...…...…...…...…...…...…...…...…...…...…...…...…...…...65 2. 6. 4. 4 Thermal Isolation Structures …...…...…...…...…...…...…...…...…....…...….....66 2. 6. 4. 5 Thermal Cross-Talk …...…...…...…...…...…...…...…...…...…...…...…...…....…......68 2. 6. 5 ““Unwanted”” Lateral Actuation of the Probes …......…...…...…...…...…...…...69 2. 7 Summary …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….......73 3 Piezoresistive and Capacitive Sensors …...…...…...…...…...…...…...….........75 3. 1 Specifications and Objective …...…...…...…...…...…...…...…...…...…......…...…......75 3. 2 Piezoresistive Sensors …...…...…...…...…...…...…...…...…....…...…...…...…...…...…......76 3. 2. 1 Background …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......76 3. 2. 1. 1 Piezoresistive Effect …...…...…...…...…...…...…...…...…...…...…...…...…...…......77 3. 2. 1. 2 Temperature Coefficient of Resistance Effect …...…...…...…...…...80 3. 2. 1. 3 Combined PZR and TCR Effects …...…...…...…...…...…...…...…...…......85 3. 2. 2 TCR Effect of CMOS Polysilicon Resistors …...…...…...…...…...…...…...…....85 3. 2. 3 Simplified Piezoresistive Sensor Analysis …...…...…...…...…...…...…...…...…...93 3. 2. 4 Preliminary Piezoresistive Test ….....…...…...…...…...…...…...…...…...…...…..........96 3. 2. 5 Thermal Boundary Conditions …......…...…...…...…...…...…...…...…...…...…........102 3. 2. 6 Sensor Design Concept …...…...…...…...…...…...…...…...…...…...…...…...…...…...…......104 3. 3 Sensor Characterization …...…...…...…...…...…...…...…...…...…...…...…......….......107 3. 3. 1 Sensor Characterization …...…...…...…...…...…...…...…...…...…...…...…...…...…...….....107 ____________________________________________________CMOS-MEMS Probes vi 3. 3. 2 Noise Analysis …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...109 3. 3. 3 Thermal Boundary Condition Change Analysis …...…...…...…...…...…....115 3. 3. 4 Thermal Boundary Condition Compensation …...…...…...…...…...…...…....117 3. 3. 5 Hysteresis Analysis …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....119 3. 3. 6 Upgraded Probe Design …...…...…...…...…...…...…...…...…...…...…...…...…...…...….....120 3. 3. 7 Contact Point Shift Test …...…...…...…...…...…...…...…...…...…...…...…...…...…...….....121 3. 3. 8 Long-Term Test …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....125 3. 3. 8. 1 Temperature Cycling …...…...…...…...…...…...…...…...…...…...…...…...…...…...133 3. 3. 8. 2 Long-Time Test with DC Drives …...…...…...…...…...…...…...…...….....134 3. 3. 8. 3 Long-Time Test with Square-Wave Drives …...…...…...…...….....135 3. 3. 9 Probe Recheck after Drift Test …...…...…...…...…...…...…...…...…...…...…...…......140 3. 3. 10 Long-Time Low Drive Test …...…...…...…...…...…...…...…...…...…...…...…...….....143 3. 3. 11 Load Force Drift Test …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...144 3. 3. 12 Combined Low ET Actuation and Load Force Drift Test …...…...145 3. 3. 13 High Resistivity Unsilicided Polysilicon Resistor Test …...…...…...146 3. 3. 14 Summary …...…...…...…...…...…...…...…...…...…...…...…...….....…...…...…...…...…...…...…....147 3. 4 Capacitive Sensors …...…...…......…...…...…...…...…...…...…...…...…...…...…...…...…...149 3. 4. 1 Working Theory for CBCM …...…...…...…...…...…...…...…...…...…...…...…...…...…...150 3. 4. 2 Capacitive Sensor Design …...…...…...…...…...…...…...…...…...…...…...…...…...…......152 3. 4. 3 Capacitive Sensor Simulation …...…......…...…...…...…...…...…...…...…...….........152 3. 4. 4 Noise Analysis …...…...…...…...…...…...…...…....…...…...…...…...…...…...…...…...…...…......154 3. 4. 5 Summary …...…...…...…...…...…...…...…...…...…....…...…...…...…...…...…...…...…...…...…......156 3. 5 Summary …...…...…...…...…...…...…...…...…......…...…...…...…...…...…...…...…...…...…......157 ____________________________________________________CMOS-MEMS Probes vii 4 Electrical Contact …...…...…...…...…...….....…...…...…...…...…...…...…...…...….........158 4. 1 Specifications and Objective …...…...…...…...…...…...…...…...…...…...…...…...…...158 4. 2 Modeling of Probe Reconfiguration Circuit …...…...…...…...…...…...…...159 4. 3 Modeling of Electrical Contact …...…...…...…...…...…...…...…...…...…...…...…...160 4. 4 Electrical Contact Processing…...…....…...…...…...…...…...…...…...…...…..........164 4. 4. 1 Electroless Nickel Plating …...…...…...…...…...…...…...…...…...…...….....…...…...…....165 4. 4. 2 Tip-Platform Platinum Sputtering …...…...…...…...…...…...…...…...…...…...…......171 4. 5 Repeatability and Reliability …...…...…...…...…...…...…...…...…...…...…...…...…...181 4. 6 Vibration in Test-Stand …...…...…...…...…...….......................................184 4. 7 Current Carrying Tests in Routing Paths …...…...…...…...…...…............187 4. 7. 1 Electromigration …...…...…...…...…...…...…...…...…...…...…...….....…...…...…...…..........187 4. 7. 2 Connection Failure in CMOS-MEMS Structures …...…...…...…..........188 4. 7. 3 DC Current Carrying …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......191 4. 8 Current Carrying Tests in Tip-Closed Circuit …...…...…...…...….....…...197 4. 8. 1 DC Current Carrying …...…...…...…...…...…...…...…...…...…...…...…...…...…...…..........197 4. 8. 2 Current Pulse Carrying …...…...…...…...…...…...…...…...…...…...…...…...…...…...…......200 4. 8. 3 Electromigration Check with Optical Microscope/SEM …...…...…...201 4. 8. 4 Electromigration Summary …...…....…...…...…...…...…...…...…...…...…...…...…...…...202 4. 9 Summary ….....…...…...…...…...…...…...…...…......…...…...…...…...…...…...…...…...…...…....204 5 Conclusions and Future Work ..…...…...…...…...…...…...…...…...…...….........205 5. 1 Open Engineering Issues …....…...…...…...…...…...…...…...…...…...…...…...…...…....205 ____________________________________________________CMOS-MEMS Probes viii 5. 1. 1 Introduction …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....205 5. 1. 2 Probe Clearance …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....205 5. 1. 3 Vertical Curl Management …....…...…...…...…...…...…...…...…...…...…...…...…...…....209 5. 1. 4 Thermal Management …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....209 5. 1. 5 Piezoresistive Sensor Optimization …...…...…...…...…...…...…...…...…...…...…...210 5. 1. 6 Probe Contacts …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...210 5. 1. 7 Mechanical Fritting (Vertical and Lateral Vibration) …...….....…......211 5. 1. 8 Probe Rough Registration …...…...…...…...…...…...…...…...…...…...…...…...…...…......212 5. 1. 9 Probe Chip Packaging …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....213 5. 1. 10 Probe Fine Alignment through Navigation …...…...…...…...…...….....…....214 5. 1. 11 Summary …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…......214 5. 2 Conclusions and Future Work …....…...…...…...…...…...…...…...…...…...…...…....214 5. 2. 1 Conclusions …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…....215 5. 2. 2 Difficulties and Challenges …...…...…...…...…...…...…...…...…...…...…...…...…...…....215 5. 2. 3 Future Work …...…...…...….....…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....215 Bibliography …...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...…...….....…....217 ____________________________________________________CMOS-MEMS Probes