[Design and Analysis of Test Structures for Measuring Stress]

by

ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

Signed __________________ Date _________________

ABSTRACT

A wafer-scale encapsulated DC-contact RF MEMS switch with a stress-reduced corrugated diaphragm is proposed and developed. The design, fabrication and characterization aspects of the MEMS switch are presented in this paper. The introduction of corrugation is proven to be an effective and easier way to reduce the residual stress in the diaphragm as compared to the approach by the stress control in the thin film deposition process. The measured pull-in voltage of the MEMS switch is significantly reduced from 105 V for a flat diaphragm to 51 V and 42 V for two-corrugation and four-corrugation diaphragms, respectively, which agree well with the calculation results by derived analytical equations. The estimated equivalent stresses in the two corresponding corrugated diaphragms are 11.9 MPa and 5.9 MPa, respectively, which are much lower than 56 MPa in the flat diaphragm. The fabricated MEMS switch can operate well, achieving more than 1 billion switching cycles for signal currents below 1 mA. The RF performance of fabricated switches was also characterized. The isolation is below -30 dB up to 5 GHz, and about -22 dB at 15 GHz. The insertion loss is about -0.8 dB up to 4 GHz, and -2.9 dB at 15 GHz.

TABLE OF CONTENTS

ACKNOWLEDGEMENTII

DECLARATIONIII

ABSTRACTIV

CHAPTER 1: INTRODUCTION1

1.1Background Of The Research1

1.2Aim of the research3

1.3Problem Statement4

CHAPTER 2: LITERATURE REVIEW6

2.1Fabrication Process Steps7

2.2Stress Measurement from Devices9

2.3Super Conducting Magnets9

2.4Bragg reflection11

2.5GaAs MESFETs17

2.6Mesfet Fabrication17

2.7Generation Current23

2.8X-Ray Topography25

2.9Metallic Bonding27

2.10Material Property Control in PVD33

2.11Surface Micromachining for Cantilever Structures35

2.12Application for Advanced Packaging37

2.13New Microinductor Device39

2.14CGS principle42

CHAPTER 3: METHODOLOGY50

3.1Design considerations50

3.2Corrugated diaphragm51

3.3Actuation voltage54

3.4Device fabrication57

CHAPTER 4: RESULTS AND ANALYSIS59

4.1Diaphragm deflection59

4.2Pull-in voltage60

4.3Life-time61

4.4RF performance62

CHAPTER 5: CONCLUSION63

REFERENCES66

CHAPTER 1: INTRODUCTION

Background Of The Research

Achievable off-state standoff voltages of a switch cell are investigated through experimental measurements of electrical breakdown in micron-sized air gaps. Breakdown voltages exceeding 300 V are demonstrated across clean air gaps as small as 0.5 µm. Based on this, design theories and criteria are discussed for power switching applications. The goals for this application are low on-state resistance, low power consumption, high current capacity, and high off-state standoff voltage. Common geometries and actuation mechanisms for MEMS actuators are compared and the electrostatic actuation of a diaphragm switch cell is chosen because of its low actuation voltage and power, its compatibility with mainstream CMOS processing technologies, and its good thermal performance. Pneumatic actuation is used as a secondary tool for the validation of diaphragm integrity. The mechanical analysis of axisymmetric thin plates is studied and two diaphragm designs are proposed: a single-crystal silicon diaphragm of uniform thickness and a highly-tensile-stressed LPCVD nitride ...