Integration of surface-micromachined zinc oxide sensors in n-well CMOS technology

Integrated sensors based on zinc oxide thin-film sensor technology have been fabricated in a 2- mu m n-well CMOS process. Diagnostic surface-microsensor structures for detecting temperature change (such as that due to infrared radiation) and force (such as that due to acceleration) have been integrated with on-chip analog CMOS signal processing electronics. These structures are formed of thin films of pyroelectric and piezoelectric zinc oxide deposited on phosphorus-doped polysilicon membranes supported 1.2 mu m above the silicon substrate. The ability to fabricate these surface microstructures in a planar process through a combination of wet chemical etching of a sacrificial oxide spacer and dry etching of a polysilicon support membrane may represent a significant improvement in ease of fabrication, yield, and reliability over previous sensor fabrication techniques based on anisotropic etching of silicon. The ability to fabricate these microsensors in a CMOS process may lead to direct integration of ZnO-based microsensors with standard analog and digital building blocks.<>