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...[ Read more ]

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.