MEMS-based step-up voltage conversion for comb-drive actuation

119 Pages·2010·5.08 MB·English

Master’s Thesis
MEMS-based step-up voltage conversion
for comb-drive actuation
by
Jarno Groenesteijn
Transducer Science and Technology Group
University of Twente, The Netherlands
Supervisors: Graduation Committee:
Dr. Ir. L. (Leon) Abelmann Prof. Dr. M.C. (Miko) Elwenspoek
Ir. J.B.C. (Johan) Engelen Dr. Ir. L. (Leon) Abelmann
Dr. Ir. R.A.R. (Ronan) van der Zee
Ir. J.B.C. (Johan) Engelen
September 15, 2010
2
Title:
MEMS-based step-up voltage conversion for comb-drive actuation
Author:
J. (Jarno) Groenesteijn
Master’s Thesis defense:
September 24, 2010
Carr´e, Ca2186 (Lecture Hall 2N)
Graduation Commitee:
Prof. Dr. M.C. (Miko) Elwenspoek University of Twente, EEMCS, TST
Dr. Ir. L. (Leon) Abelmann University of Twente, EEMCS, TST
Ir. J.B.C. (Johan) Engelen University of Twente, EEMCS, TST
Dr. Ir. R.A.R. (Ronan) van der Zee University of Twente, EEMCS, ICD
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4
Abstract
This report is the result of the master’s thesis of Jarno Groenesteijn. Theoretical and practical
research has been done on a voltage step-up converter based on a comb-drive to investigate the
possibilities of this new kind of converter. An analytical analysis has been done to predict the
operation of a converter like this. The analytical description is used to make a computer model
topredictthemechanicalandelectricalbehaviouroftheconverter. Eightdifferentteststructures
are designed and fabricated to test the operation of the converter and to improve the quality of
the computer model. Measurement on the mechanical behaviour of the comb-drives have been
combined with finite element simulations on the electrical behaviour of the comb-drives to find
an accurate computer model of the voltage step-up converter. Analysis has been done to find
the most important elements that reduce the performance of the converter and solutions to these
problems have been proposed.
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6 ABSTRACT
Acknowledgements
This project started of in the heads of my supervisors Johan Engelen and Leon Abelmann and
without their enthusiastic support, the project would never have been this complete.
I would also would like to thanks Theo Lammerink, Gijs Krijnen, Remco Wiegerink and Niels
Tas for donating chip area on the wafers for the MEMS Design course to my project and Meint
de Boer for fabricating more working chips then I could measure.
CreditgoestoRemcoSandersforhisexpertiseandworkonthevibrometerandvacuumcham-
ber. Withouthishelp,Iwouldnothavebeenabletospendsomuchtimeonactualmeasurements.
And last but not least, I would like to thank my fellow TST students: Jaap Kokorian, Tjitte-
JeltePeters,HenrideJong,MichelZoontjesandKoertVergeerfortheirtalk,theirinsightfulideas
and for the group trips to the coffee machine.
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8 ACKNOWLEDGEMENTS
Contents
Abstract 5
Acknowledgements 7
1 Introduction 11
2 Theory 13
2.1 Theoretical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.1 Output voltage and current . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3 Device design 19
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2 Simulation and design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.1 The Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3 Simulation of final designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.4 20Sim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 Simulations of the updated model. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3.1 The Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.4.1 Design overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.2 Spring Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.3 Snap-in to the bulk. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4.4 The different mask designs . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4.5 Final Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.4.6 Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.4.7 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4 Experiments 47
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.2 Output specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.3 Mechanical behaviour of the converter . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4 Actuation electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.4.2 Parasitic impedances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.4.3 The Micro Controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.4 Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.4.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.5 Leakage and parasitics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
5 Discussion 59
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10 CONTENTS
6 Conclusion 61
7 Recommendations 63
7.1 Improvements on current design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.1.1 Back-etch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
7.1.2 The wafer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.1.3 The electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.1.4 Other improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.2 Other options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Bibliography 67
A Tables 69
A.1 Device Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.2 Experiements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
B Figures 75
B.1 Device Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
C 20-Sim code 81
C.1 SignalGenerator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
C.2 Comb-Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
C.2.1 Version 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
C.2.2 Version 2: including stator capacitance. . . . . . . . . . . . . . . . . . . . . 84
C.3 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
C.3.1 Version 1: Initial model (resistor only) . . . . . . . . . . . . . . . . . . . . . 87
C.3.2 Version 2: Variable resistors and capacitors . . . . . . . . . . . . . . . . . . 87
C.4 Cbuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
C.5 Vsource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
C.6 Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
C.7 Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
C.8 Damper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
C.9 Rleakage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
C.10Roxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
D MatLab code for Comsol 91
D.1 find cap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
D.2 build struct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
D.3 getpolyfit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
E MatLab code for CleWin 97
E.1 Build Comb Bank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
E.2 function Build DC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
E.3 function Build FF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
E.4 function DC Build Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
E.5 function FF Build Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
E.6 function Finger Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
E.7 function Lightning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
E.8 function PerfBox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
E.9 Set Comb variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
F MicroController code 117
F.1 Main . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117