Design of Capacitive Displacement Sensors for Chip Alignment
- Slides: 37
Design of Capacitive Displacement Sensors for Chip Alignment Jose Medina Professor N. Mc. Gruer Center for High-rate Nanomanufacturing
Outline 1. 2. 3. 4. 5. 6. 7. 8. Introduction Displacement sensors Capacitive sensors FEM simulations Readout circuit Scaled models Experiments Conclusions Center for High-rate Nanomanufacturing
Introduction 2 Approach 1. Assemble 2. Alignment 3. Transfer Center for High-rate Nanomanufacturing
Introduction • Requirements – – Accuracy to nm Cost effective Fast Compatible • Fabrication • Electronics • Actuator (nanopositioner) – Variable gap – Connections to only one side Center for High-rate Nanomanufacturing
Displacement Sensors Criteria Probe-based Optical Thermal Capacitive Accuracy ++ ++ +/+ + Range - /+ ++ +/+ + Speed + + - + Fabrication - -- ++ ++ Electronics integration + - ++ ++ - /+ ++ -/+ -- +/+ + -/+ + ++ Parasitic forces Power consumption A. A. Kuijpers, ‘Micromachined Capacitive Ling-Range Displacement Sensor for Nanopositioning of Microactuator Systems’, Ph. D thesis, Universiteit Twente Center for High-rate Nanomanufacturing
Capacitive sensors Capacitive sensor literature – Widely used • Drug delivery, temperature/humidity sensors, automotive, positioners – No sensor moves in two dimensions ‘Modeling and Optimization of a Fast Response Capacitive Humidity Sensor’, Tetelin Center for High-rate Nanomanufacturing ‘Perspectives on MEMS in Bioengineering: A Novel Capacitive Position Microsensor’, Pedrocci
Capacitive sensors Electrodes on substrate and template Center for High-rate Nanomanufacturing
Capacitive sensor C=Q/V=f(geometry) ~ Chip alignment: connections only on one electrode Center for High-rate Nanomanufacturing
Capacitive sensor Complete system Equivalent circuit Center for High-rate Nanomanufacturing
Capacitive sensor Cantor set geometry – First level – Second level – Third level Center for High-rate Nanomanufacturing
Capacitive sensor Central fractal geometry – First level – Second level – Third level Center for High-rate Nanomanufacturing
FEM simulations Numerical method A. Hiekes, SIEMENS; Baxter, Capacitive Sensors Center for High-rate Nanomanufacturing
FEM simulations Modeling scenarios • Closed system • Open boundary – Natural boundary condition – Trefftz domain – Infinite elements ANSYS, Inc Center for High-rate Nanomanufacturing
FEM simulations Center for High-rate Nanomanufacturing
FEM Simulations Models – Doped Si substrates – Glass top substrate – Glass bottom substrate Center for High-rate Nanomanufacturing
Readout Circuit Converter – transforms a signal to another more convenient Voltage applied at capacitor Center for High-rate Nanomanufacturing
Readout circuit Alignment precision and converter performance Circuits – Oscillator – AC-bridge – Transimpedance amplifier – Switched-capacitor – Sigma-Delta modulator Center for High-rate Nanomanufacturing
Readout circuit Transimpedance amplifier Synchronous demodulator Low pass filter Center for High-rate Nanomanufacturing
Readout circuit Switched-Capacitor Amplifier φ1 φ2 Center for High-rate Nanomanufacturing
Readout circuit Sigma-Delta modulator Cap-to-digital converter based on SC Center for High-rate Nanomanufacturing modulator
Scaled Models Scaled models – How do and C scale with geometry? Center for High-rate Nanomanufacturing
Scaled Models Theoretical accuracy Scaled models Center for High-rate Nanomanufacturing
Experiments Two PCBs – Large w/g ratio • Max accuracy? – Small w/g ratio • Geometry performance? Short w/d ratio Top board Central. Large group Width Top board 0. 03’’ w/d ratio (mm) Spacing traces 0. 03’’ Trace width 0. 12’’ 3. 048 cm Spacing subgroups 0. 09’’ Separation traces 0. 12’’ 3. 048 cm Lateral group Width 0. 15’’ (mm) Separation groups 0. 36’’ 9. 144 cm Spacing traces 0. 15’’ Spacing groups 0. 45’’ Bottom board 0. 762 0. 06’’ 1. 524 Bottom board 0. 762 0. 03’’ 0. 762 0. 25’’ 6. 350 cm 2. 286 0. 12’’ 3. 048 0. 47’’ 11. 938 cm 3. 81 0. 3’’ 7. 62 3. 81 11. 43 0. 54’’ 13. 716 Center for High-rate Nanomanufacturing
Experiments Setup – Stage – PCBs – Readout circuit • AD 7745 – Connectors, wires – Computer Center for High-rate Nanomanufacturing
Experiments Results: large feature board • Experiments greater capacitance • Sim and experiments same profile • Experiments different results • Accuracy – 5 f. F (specs 4 f. F) – 0. 1 mm (calculations 2 μm) • Sim/exp results further for long displacements Center for High-rate Nanomanufacturing
Experiments Results: small feature board • Cap increases with displacement! • Similar profiles • Good performance at short gap • Min largest gap 3 mm (u=0. 762 mm) Center for High-rate Nanomanufacturing
Conclusions Simulations – DC capacitance • Ground close than at infinite • 5 electrodes + stage – Sim/exp further for large gaps • Cap to stage dominant – Variations between experiments • Plates not parallel, gap varies – Increase cap with displacement • C 13 and C 23 decrease • C 12 dominant, board ‘perturbs’ E Center for High-rate Nanomanufacturing
Conclusions Sensor design suggestion – Central fractal geometry – Width depends upon min/max gap • Min: g/w < 1/3 for last level to take over, ideally <1/10 • Max: g/w < 1 to avoid instabilities – Capacitor width w, #levels u – Chip 15 x 15 mm sq sensor 0. 5 x 0. 5 mm sq Center for High-rate Nanomanufacturing
Conclusions Min feature size 1 um 0. 1 um w strip-group 1 1 -3 um 100 -300 nm 1 -3 um w strip-group 2 1 -15 um 0. 1 -1. 5 um 1 - 291 um w strip-group 3 5 -75 um 0. 5 -7. 5 um 0. 1 – 1. 5 mm w strip-group 4 25 -375 um 2. 5 -37. 5 um 0. 125 -1. 875 mm 12. 5 -187. 5 um w strip-group 5 w strip-group 6 0. 0625 -0. 9375 mm Max gap 25 um 0. 1 mm Min gap 20 nm 10 nm 20 nm Max gap 25 um 0. 1 mm #sets n 5 7 9 49+2 Xmin scaled 240 nm 34 nm 26 nm 5. 8 nm Xmin calculated 4. 8 nm 0. 68 nm 0. 53 nm 0. 11 nm Center for High-rate Nanomanufacturing
Thank you for you attention Acknowledgments – Advisor: Professor Mc. Gruer – Professors: Adams, Busnaina, Muftu, Papageorgious, Sun – Students: Prashanth, Juan Carlos Aceros, Peter Ryan, Andy Pamp, Siva, Harris Mussolis Center for High-rate Nanomanufacturing
Capacitive sensors Definition Capacitance Conductor a + + + +++++++++++++++ e- Vs - - - - - Conductor b Center for High-rate Nanomanufacturing
FEM Simulations Convergence Center for High-rate Nanomanufacturing
Center for High-rate Nanomanufacturing
Switched-Capacitor amplifier Sampling phase (φ1 (φ on, φ2 φoff) • • Charge-transfer phase 1 off, 2 on) φ1 φ2 Center for High-rate Nanomanufacturing
Correlated Double Sampling • Processing Sampling phase Center for High-rate Nanomanufacturing
Simulations switched-capacitors V (volts) Time (ms) Center for High-rate Nanomanufacturing
Bandwidth switched-capacitors Center for High-rate Nanomanufacturing
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