Miniaturization and integration of accelerometers in standard integrated circuit (IC) processes has been the topic of extensive research. In most cases, accelerometer structures involve a solid proof mass that is allowed to move under accelerating conditions. This approach has many disadvantages. One key disadvantage is the difficulty of processing such components in IC technologies inherently unsuited for these components.
Micromachining techniques have brought about many novel miniaturized accelerometer structures, although the fabrication process includes many masks and etching steps. One aspect of the invention concerns the integration of accelerometer devices in complementary metal-oxide semiconductor (CMOS) technology, where on-chip drive and sense circuitry is available, and overall costs are lower. Because of these advantages of CMOS technology, many other classes of sensors have been implemented in CMOS by simple post-processing micromachining.
An improved method of manufacturing convector accelerometers and tilt sensors using CMOS technology has been developed. The method fabricates large quantities of convector accelerometers and tilt sensor devices in standard ICs by patterning temperature sensing and heater elements in parallel on a common substrate, and then carrying out the maskless etching operation for all devices at the same time. This fabrication process enables a concept for acceleration and tilt sensing devices that uses the acceleration of natural heat convection from heated resistive wires in a gas surrounding the device instead of measuring the acceleration of a solid proof mass. This invention integrates accelerometer devices in CMOS technology, where on-chip drive and sense circuitry are available, and overall costs are low.
The convective accelerometer and tilt sensor device made by this method uses thermocouples as the temperature sensing elements. This approach provides significant benefits. It enables batch fabrication of the sensor devices wherein a very large number of the temperature sensing and heater elements of the devices are first patterned in parallel on a common substrate, and the maskless etching operation is carried out for all devices at the same time.