Microfabrication of variable range and multi-directionally sensitive thermal flow sensor

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] This investigation reports the design, computational simulation, fabrication and characterization of a variable range and multi-directionally sensitive micromachined thermal flow sensor based on amorphous germanium thermistors. For measuring various flow ranges and flow directions with a single device, twelve thermistors are placed on an 2 x 2 mm supporting square shaped dielectric membrane made with silicon nitride. The thermistors are located at different distances from a central micro-heater that is made with a bilayer of Ti/Pt and can be driven to 200 degrees C with about 580 mW applied power. The thermistors are laid as six pairs on the aforementioned substrate with three pairs located along the X axis and another three pairs located along the Y axis. Optimized design for thermistor locations is provided by conducting two-dimensional finite element analysis (FEA) utilizing ANSYS Fluent software and the influence of thermistor locations on the sensitivity of device is presented. Numerical results and characterization of the device show its successful performance for detecting flows in the range from 100 ? m/s to 20 m/s, working at constant heater temperatures from 150 degrees C down to 70 degrees C and constant heater power less than 580mW. Also, the maximum angle error is determined to be 5.5 degrees.