A multi-element monolithic mass flowmeter with on-chip CMOS readout electronics

This paper reports the implementation of control circuitry for a multi-element mass flow sensor capable of simultaneously measuring five different gas-related parameters necessary for mass flow. A process has been developed to merge the micromachined sensing structures and the CMOS readout circuitry on a single chip. The total process requires thirteen masks: eight for the double-poly single-metal CMOS process and five for additional processing of the transducer elements. The on-chip circuitry includes offset-free instrumentation amplifiers, an analog multiplexer, heater drive circuits, self-test circuitry, and a band-gap temperature sensor using substrate npn bipolar transistors. The resulting multi-element chip requires only ten external pins and delivers high-level buffered output signals describing gas velocity, type, direction, pressure, and temperature. The chip dissipates 120mW from is ±5V supplies and measures 3.5mm ×5mm in 3¼m features.