Piezoresistive Element
A semiconductor component changes its electrical resistance in response to mechanical strain and maintains its functionality at extreme temperatures. Utilizing silicon carbide piezoresistors allows for the creation of pressure sensors that operate in environments where standard silicon would fail. These elements are typically integrated into micro-electro-mechanical systems for aerospace and geothermal exploration.
Thermal Advantage
The wide bandgap of the material prevents the thermal generation of carriers that would otherwise swamp the signal at high temperatures. While silicon becomes conductive and loses its sensing ability above two hundred degrees Celsius, these carbide structures remain effective well beyond five hundred degrees. This property enables direct measurement of engine combustion or deep-well pressures.
Fabrication Technique
Manufacturing involves the growth of epitaxial layers followed by ion implantation to define the resistive regions within the crystal. Deep reactive ion etching is then used to create the diaphragms or beams that will experience the mechanical strain. Achieving a low-resistance ohmic contact at the junctions is a substantial challenge that requires specialized metallization schemes.
If the contact degrades, the resulting noise and drift will mask the small resistance changes caused by the strain.
Signal Integrity
Precise measurement depends on a high gauge factor and low noise floors. Designers optimize the doping levels to maximize sensitivity while minimizing the temperature coefficient of the resistance.
