Silicon-on-sapphire wafers are formed by depositing silicon onto the sapphire substrate at very high temperatures. Natural sapphire tends to contain impurities, so very pure sapphire crystal is grown in a controlled lab environment. The formed sapphire ingots are cut at a 57° angle. This is known as the R-Plane. This plane reveals the oxygen atoms in the crystal and because the spacing of these atoms is almost identical to that in a silicon crystal, the silicon can be cleanly deposited onto the surface of the sapphire wafer.
Doped silicon strain gauges are etched from the layer of silicon and individual strain gauges are electrically isolated from each other by the outstanding insulating characteristics of the sapphire substrate. The ability to operate at high temperatures, chemical inertness, and virtual absence of hysteresis make the strain gauges ideal for use in pressure sensors.
Utilising Silicon-on-Sapphire sensing technology results in excellent long-term stability of <0.2% and also has a major advantage over non-SOS bonded silicon sensors. The silicon Wheatstone bridge formed during the manufacture is free from any residual stresses that may add to hysteresis and non-repeatability errors, which decrease long-term stability. There are no bonding agents between the sensing element and sapphire substrate that may age and cause instability.