Rolf Kobs

Temperature-independent pressure sensors using polycrystalline silicon strain gauges

Abstract The sheet resistance and piezoresistive effect (k-factor) and their temperature coefficients for LPCVD-polysilicon films are examined as a function of the boron concentration and the averaged grain size. In particular, heavily boron-doped polysilicon strain gauges show a TCR of +0.1%/K and a TCk of −0.1%/K. Using a constant current supply for a Wheatstone bridge, a nearly complete temperature compensation of sensitivity can be realized. We show results of pressure sensors with a temperature deviation of only 0.2%/10K without any external compensation network.

Noise Properties of NbN-MgO-NbN SQUIDs

DC-SQUIDs made of refractive materials NbN-MgO-NbN were prepared using thin film preparation techniques. The noise properties of these SQUIDs were investigated. The white energy sensitivity of typical devices is 600h (8mF0/AHz). The measured values are compared with theoretical predictions and the standard optimization rules. The low frequency noise was measured directly and using different modulation schemes. The SQUIDs show a relatively high 1/f noise onset in the range of 100Hz. The main contribution comes from out-of-phase critical current fluctuations and can be effectively suppressed by bias modulation.