We present a four point bending setup suitable for high precision characterization of piezoresistance in semiconductors. The compact setup has a total size of 635cm3. Thermal stability is ensured by an aluminum housing wherein the actual four point bending fixture is located. The four point bending fixture is manufactured in polyetheretherketon and a dedicated silicon chip with embedded piezoresistors fits in the fixture. The fixture is actuated by a microstepper actuator and a high sensitivity force sensor measures the applied force on the fixture and chip. The setup includes heaters embedded in the housing and controlled by a thermocouple feedback loop to ensure characterization at different temperature settings. We present three-dimensional finite element modeling simulations of the fixture and discuss the possible contributions to the uncertainty of the piezoresistance characterization. As a proof of concept, we show measurements of the piezocoefficient π44 in p-type silicon at three different doping concentrations in the temperature range from T=30°CtoT=80°C. The extracted piezocoefficients are determined with an uncertainty of 1.8%.
This paper presents experimental results of the piezoresistance in p-type tensile strained silicon and compressive strained silicon germanium grown by molecular beam epitaxy (MBE) on (001) silicon substrates. The piezoresistance decreases in a tensile strained layer and increases in a compressive strained layer when compared to the unstrained material. The results show that one can tune the piezoresistance by tuning the strain in the piezoresistor and thus tailor the performance of the device. The obtained results show an increase in the piezoresistance effect of 35% in compressive strained silicon germanium and a decrease in the piezoresistance effect in tensile strained silicon of 24%. Furthermore, the results show that the piezoresistance of a tensile strained silicon crystal has a smaller temperature dependency compared to that of unstrained silicon. The piezoresistance effect decreases by 7% in tensile strained silicon compared to the piezoresistance effect decrease in silicon of 18% when changing the temperature from 30 o C to 80 o C.Mater. Res. Soc. Symp. Proc. Vol. 958
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