A 1200-atmosphere bulk-type all-silicon pressure sensor

Trench-Isolated Bulk-Type Pressure Sensor on Silicon-on-Insulator for High-Temperature and High-Pressure Downhole Applications

“…Two orthogonal pairs of piezoresistors respectively aligned to the 001 and 11 0 orientations are realized in the center region on the sensor-side of the vacuum cavity and electrically configured to form a Wheatstone bridge. The relative change of the resistivity ∆ρ' 11 /ρ along the longitudinal direction of a piezoresistor is given by [2] ∆ρ' 11 ρ = π' 11 σ' 11 + π' 12 σ' 22 + π' 16 σ' 12 ≈ π' 11 σ' 11 + π' 12 σ' 22 , (1) where π' 11 , π' 12 and π' 16 are the respective longitudinal, transverse and shear piezoresistive coefficients and σ' 11 , σ' 22 and σ' 12 are the respective longitudinal, transverse, and shear stress components. Furthermore, σ' 12 is small enough to be neglected under hydrostatic pressure loading conditions [2].…”

“…Furthermore, σ' 12 is small enough to be neglected under hydrostatic pressure loading conditions [2]. For the piezoresistors isolated and bound by the completelyfilled narrow trenches, the relative change in the longitudinal resistivity is given by (1). For those isolated by the partially-filled wide trenches, σ' 22 can be largely relieved by a proper design of the trench dimensions, thus reducing the biaxial stress field to a uniaxial stress field.…”

“…While MEMS pressure sensor with its relatively low cost and small size has the potential to replace the resonant quartz pressure sensor, it is still hindered by a number of limitations. A recent attempt [1] has been made to address some of the issues by replacing the conventional diaphragm-type with a bulk-type pressure sensor to handle the targeted high-pressure load (≥ 200 MPa), but the junction-isolation of the piezoresistors must be replaced by the presently demonstrated dielectric-isolation to handle the anticipated high operating temperature (≥ 200 °C). A higher pressure sensitivity is desirable for reducing the electrical offset and its associated temperature coefficient.…”