HIGH-SENSITIVITY 2-D FLOW SENSOR WITH AN ETCHED THERMAL ISOLATION STRUCTURE

This paper describes a two-dimensional thermal flow sensor, fabricated by silicon planar technology and subsequent micromachining. Using a two-step etching process, a thermally isolated floating-membrane structure has been formed in the chip. Flow is measured by detecting flow-induced temperature differences in two directions on the heated membrane, and this principle allows directional flow measurements over the full range of 360°. When compared to a wafer-thick silicon flow sensor of similar dimensions, this new structure possesses a much higher sensitivity, and an improved offset and time response behaviour. The response time for the behaviour of the average membrane temperature is found to be of the order of 150 ms, while for the temperature-difference measurement mode the response time is estimated to be only 14 ms. First experiments show a typical error of 3° in predicted flow angle, and 5% in flow velocity. © 1990.