Design and fabrication of single-chip intelligent silicon thermal flow sensors in standard CMOS technology

Thermal flow sensors which use thin film thermistors in a micro-bridge are considered, and configurations which yield optimum sensitivity, power consumption and frequency response are identified. The different biasing modes and transduction mechanisms are also described. The mask layout design and post-process micromachining step is illustrated for a commercial CMOS process, and low-cost packaging methods are suggested. Integration of interface electronics and signal processing on the same chip as the sensor elements offers many advantages, including improved immunity from interference, reduced interconnection cost and the possibility for complete systems on a chip. As a consequence the performance requirements for the sensor interface circuitry are relaxed. Silicon thermal flow-sensors with integrated interface electronics are presented. These have been fabricated in a standard low-cost 2.0 micron double polysilicon, double metal CMOS technology, using a single additional process step demonstrating the feasibility of implementing a complete intelligent sensor system on a single chip at minimal cost.