Zusammenfassung ................................................. I
Abstract ...................................................... III
Abbreviations .................................................. IV
1 Introduction ................................................. 1
1.1 Motivation .............................................. 1
1.2 State of the Art ........................................ 4
1.2.1 Wireless SAW Sensor System ....................... 4
1.2.2 Impedance-loaded SAW Sensors ..................... 5
1.2.3 Analytic Methods for SAW Devices ................. 5
1.3 Objectives .............................................. 8
1.3.1 Simulation of Impedance-loaded SAW Sensors ....... 8
1.3.2 Combination with VHDL-AMS ........................ 8
1.3.3 Optimizing Design ................................ 9
1.4 Scope of the Work ....................................... 9
2 SAW Background .............................................. 11
2.1 IDTs and Delay Line .................................... 11
2.2 Behavior in Periodic Structures ........................ 13
2.2.1 Bragg Reflection ................................ 13
2.2.2 Stopband ........................................ 15
2.2.3 Energy Storage Effect ........................... 16
2.3 Models of SAW IDT ...................................... 16
2.3.1 ECM ............................................. 17
2.3.2 COM Model ....................................... 20
2.3.3 P-Matrix Model .................................. 25
3 Simulation of Impedance-loaded SAW Sensors .................. 28
3.1 Basic Principle ........................................ 28
3.2 S-parameters ........................................... 31
3.3 Simulation Using VHDL-AMS .............................. 34
3.3.1 Determination of Parameters ..................... 34
3.3.2 Description of ECM in VHDL-AMS .................. 40
3.3.3 ECM of Impedance-loaded SAW Sensors ............. 43
3.3.4 Result analysis of ECM .......................... 44
3.4 Simulation Using COM Model ............................. 49
3.4.1 COM Model of SAW IDT ............................ 50
3.4.2 COM Model of Impedance-loaded SAW Sensors ....... 52
3.4.3 Determination of Parameters ..................... 55
3.4.4 Result Analysis of COM Model .................... 60
3.4.5 Graphic User Interface .......................... 63
3.5 SEM Pictures of Real Devices ........................... 66
3.6 Comparison of ECM with COM Model ....................... 67
4 Design Using COM Model ...................................... 71
4.1 Basic Requirements of Impedance-loaded SAW Sensors ..... 71
4.2 Substrate .............................................. 74
4.3 Transmitting/receiving IDT ............................. 75
4.3.1 Estimation of Structural Parameters ............. 75
4.3.2 Simulation of Transmitting/receiving IDT ........ 77
4.4 Programmable Reflector ................................. 79
4.4.1 Stopband Analysis ............................... 79
4.4.2 Single-electrode-type IDT as programmable
reflector ....................................... 81
4.5 Response of the Entire SAW Chip ........................ 82
4.6 Layout of SAW Chips .................................... 83
4.7 Application to Sensors ................................. 84
4.7.1 Capacitive Sensor ............................... 87
4.7.2 Resistive Sensor ................................ 89
4.8 Parasitic Effects ...................................... 91
4.8.1 Bond Wires and Contact Poles ................... 91
4.8.2 Chip Edges ..................................... 95
5 Passive Radio Requestable SAW Sensor System ................. 97
5.1 Interrogation Unit ..................................... 98
5.2 Experimental Results ................................... 99
6 Outlook and Further Work ................................... 101
6.1 Miniaturization ....................................... 101
6.2 Full Simulation ....................................... 102
6.3 SAW ID-tags or Sensors in GHz Range ................... 104
7 Conclusions ................................................ 105
Appendix A FEMSDA ............................................ 108
A.l Introduction ...................................... 108
A.2 B10tekjaer's Theory ............................... 109
A.3 Combination with FEM .............................. 110
Appendix В Solution of COM Equations ......................... 112
Appendix С COM Parameters Including SH-type SAWs ............. 114
Acknowledgements .............................................. 117
Bibliography .................................................. 118
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