A densitometer based on a resonant silicon structure

The densitometers are made by batch fabrication. Each silicon wafer contains 16 densitometers. The densitometers are fabricated from two bonded silicon wafers and encapsulated in vacuum using two glass wafers.

The photo shows a diced densitometer chip. The size of the scale is in centimeters. The interconnecting wires to the Cr/Au electrodes are glued in place using a conducting epoxy.

The SEM shows a cross section of the densitometer. The flow channel is clearly seen as a hexagonal tube in silicon. The area surrounding the silicon tube is kept in vacuum to minimize the effects of squeeze film damping.

The electronics for actuation and detection using the burst technology specially developed for this project mounted with the sensor on a single PCB. The circuit is here built out of discreet components, but can be integrated on to an ASIC to reduce the area used for the electronics.

A bonded anisotropically etched silicon etch mask has been anodically bonded to a glass wafer. This SEM shows the effects of isotropic under etch in a Glass wafer. The walls are nearly 45 degrees as the etch rate down is almost the same as the under etch.