PhD Defense Announcement: Chia-Fang Chiang

Stanford University Ph.D. Oral Examination – Dept. of Mechanical Engineering

 

Title:

Micromachined Temperature Compensated Pressure Sensor
Implemented Using a Multi-Sensor Integration Platform

 

Speaker: Chia-Fang Chiang

Advisor: Professor Thomas W. Kenny

 

Date: Friday, December 14, 2012

Time: 10:00 am (refreshments at 9:45 am)

Location: Hartley conference center (Mitchell Earth Sciences) - Room 130

 

Abstract: 

 

Micromachined pressure sensors are widely used in our everyday lives: in automobiles they are implemented to monitor tire pressure and detect side crashes; in medical devices they are used to track blood pressure in the brain; and in navigation they are utilized to determine altitude and assist global positioning system (GPS) receivers. While the requirements for a pressure sensor vary depending upon the specific application, a common requirement is accurate sensing over a wide operating temperature range (-40 – 125 °C).

 

I will begin by introducing our capacitive pressure sensor design and demonstrating how it outperforms a piezoresistive pressure sensor with respect to temperature insensitivity. To further reduce temperature dependence, a high resolution resonant thermometer has been cofabricated with the capacitive pressure sensor, enabling the tracking of temperature fluctuations on the die and correction of the associated pressure error.

 

In the second half of the talk, I will discuss our development of a resonant pressure sensor. This is motivated by the emerging demand of altimeters which require high resolution (10Pa/meter). As the design is coupled to the die strain, the accuracy of the resonant pressure sensors is strongly influenced by errors induced by both temperature and package stress. We address this limitation with a multiple sensor solution where temperature and strain sensors are cofabricated to reduce the pressure sensor's temperature and package stress dependence, thus improving accuracy.

 

Throughout the talk, I will discuss the process flows enabling the fabrication of such structures. Key developments include time insensitive vapor etching of silicon dioxide with hydrofluoric acid to release structures as well as the fabrication of structures that can be driven and sensed in both in-plane (x,y) and out-of-plane (z) directions on either bulk silicon or SOI wafer substrates.