THESIS
2014
iii leaves, iv-xvii, 85 pages : illustrations ; 30 cm
Abstract
It is difficult for traditional micro-engineering methods to generate a suspended
structural layer for micro-electro-mechanical systems (MEMS) applications without a
releasing step. The limitation becomes more serious when it comes to integration with
electronic circuits. Various schemes proposed for MEMS-CMOS integration have
issues that either hamper design flexibility or require special care.
Silicon-Migration Technology (SiMiT) starts with the formation of an array of
“wells” using a deep reactive-ion etcher (DRIE). During a subsequent heat-treatment,
surface-diffusion of silicon leads to the coalescence of the voids at the bases of
adjacent wells and the closing of the space at the top of a well. In the end a continuous
cavity buried under a cover-diaphragm can be obtain...[
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It is difficult for traditional micro-engineering methods to generate a suspended
structural layer for micro-electro-mechanical systems (MEMS) applications without a
releasing step. The limitation becomes more serious when it comes to integration with
electronic circuits. Various schemes proposed for MEMS-CMOS integration have
issues that either hamper design flexibility or require special care.
Silicon-Migration Technology (SiMiT) starts with the formation of an array of
“wells” using a deep reactive-ion etcher (DRIE). During a subsequent heat-treatment,
surface-diffusion of silicon leads to the coalescence of the voids at the bases of
adjacent wells and the closing of the space at the top of a well. In the end a continuous
cavity buried under a cover-diaphragm can be obtained without a releasing step.
Following a brief summary of the physics, simulations and experimental results
of the initial works on SiMiT, the SiMiT process was further understood via a
self-developed front-tracking simulator. SiMiT thermal treatment was carried out
using rapid thermal annealing at 1150 °C in atmospheric pressure argon. Various
structures useful for MEMS applications including oxide micro-channels, suspended
cantilevers and diaphragms were realized using SiMiT. Potential application issues
with SiMiT were discussed, with solutions provided. The application of SiMiT to the
realization of a CMOS integrated 16×16 self-scanned active-matrix tactile sensor was
subsequently described. A sensitivity of ~0.03 μV/V/Pa and spatial resolution of ~145
“pixels per inch”, suitable for applications such as dexterous robotic manipulation,
was achieved. With the elimination of the conventional sacrificial layer etch, the
issues of material- and process-incompatibility inherently present in many integration
schemes are largely avoided. Finally, SiMiT is applied to the realization of a
differential capacitive pressure sensor with innovative diaphragm shape and reference
capacitor designs, achieving a sensitivity of ~40 aF/Pa in a ~100 kPa pressure range.
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