A maskless post-CMOS bulk micromachining process and its application

This work investigates a post-CMOS (complementary metal-oxide semiconductor) bulk micromachining process for fabricating suspended microstructures. The advantage of the post-CMOS process is easy execution with low-cost maskless wet etching. The post-CMOS process involves wet etching to remove sacrificial layers, which are stacked layers formed from metal and via layers, to expose the silicon substrate. Then, KOH solution is employed to etch the silicon substrate to develop deep cavities and generate suspended structures. Many suspended structures, which include bridges and plates, are fabricated using the post-CMOS bulk micromachining process. With the same process, two devices that are a suspended micro inductor and a micro hot plate are manufactured successfully. Experimental results reveal that the maximum quality factor of the suspended micro inductor is 4.8 at 4 GHz, and the micro hot plate can generate a high temperature of 300 degrees C with an applied voltage of 4 V, which has excellent thermal isolation and heating effect.