Design of analogue CMOS VLSI MEMS sensor : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering , Integrated Circuit Design at School of Engineering and Advanced Technology, Massey University, Albany campus
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Date
2015
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Massey University
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Abstract
There is an increasing demand of a highly sensitive and reliable pressure micro-sensor
system, for implantable and non-implantable medical applications. The prerequisite of a
miniaturized device for minimally invasive procedures, posed greater challenges in the complex
integrated design of micro-system. Micro-sensor system designs in the recent advanced CMOS
technologies are explored in this work for effective system miniaturization and improved
performance. The material choices and geometry designs, which significantly influence the
sensitivity and dynamic range of the micro-scale sensor devices, are well addressed. Cointegrations
of MEMS devices with signal conditioning circuits that effectively reduce the
parasitic effect are also performed for enhancing the overall system performance. In addition,
system reliability is also improved with on-chip metal interconnections. The employed process
technologies to a greater extent contributed to the high yield for these low cost micro-sensor
systems.
This research focuses on the design of integrated CMOS MEMS capacitive pressure sensors
for diverse bio-medical applications. Two monolithically integrated capacitive pressure microsensor
systems are designed, fabricated and experimentally verified. A novel micro-electromechanical
capacitive pressure sensor in SiGeMEMS process, vertically integrated on top of a
0.18 μm TSMC CMOS processed die is proposed. The perforated elliptic diaphragm, which is
edge clamped at the semi-major axis is developed using poly-SiGe material. High performance
on-chip CMOS conditioning circuits are also designed to achieve better overall sensitivity.
Experimental results indicate a high sensitivity of around 0.12 mV/hPa along with a nonlinearity
of around 1% for the full scale range of applied pressure load. The L-clamp spring
anchored diaphragm provided a wide dynamic range of around 900 hPa. Another integrated
capacitive pressure micro-system, developed using the advanced standard IBM CMOS process
in two geometrical designs is also proposed. A step-sided elliptic diaphragm that overcomes the
CMOS process limitations is fabricated to achieve regulated membrane deflections and
improved sensitivity. A foundry compatible post-process technique, for a lateral release length
of 125 μm is also performed successfully on the 130 nm CMOS platform. A current cross
mirroring technique is utilized to enhance the transconductance of an on-chip operational
amplifier to achieve a high single stage gain. Sensitivities of the fluorosilicate sealed absolute
pressure sensors were measured to be 0.07 mV/Pa and 0.05 mV/Pa for the elliptic and
rectangular element, respectively. In addition, the linear capacitive transduction dynamic range
was found to be 0.32 pF and 0.23 pF, respectively, for the elliptic and rectangular element.
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Keywords
Microelectromechanical systems, Pressure transducers, Metal oxide semiconductors