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In this work we demonstrate theoretically and experimentally the capability to reduce the readout noise of an optical and X-ray photon detector based on the semiconductor DEPFET device below a level of only [0.3e.sup.-] ENC (equivalent noise charge). The readout method used is called 'Repetitive Non Destructive Readout' (RNDR) and was realized by placing two single DEPFET-devices next to each other and by coupling their charge storing region by an additional gate. By transferring the stored charge from one DEPFET to the other and vice versa the same charge can be measured non-destructively and arbitrarily often. Taking the average value of a large number n of these measurements, the noise is reduced by 1/[square of (n)]. The main advantage of such a detector is to greatly reduce the contribution of the 1/f noise to the readout noise. The theoretically and experimentally achievable resolution for different operating parameters (leakage current, readout noise, number and duration of readouts) was investigated by Monte-Carlo simulations and verified on a real RNDR minimatrix (pixelarray). Single optical photon detection with high quantum efficiency and, even more fascinating, the possibility to distinguish between different numbers of photons, e.g., 100 from 101 are demonstrated in measurements. Index Terms--Active pixel sensor, DEPFET, low noise readout, Repetitive Non Destructive Readout (RNDR), single optical photon detection, sub-electron noise.

A continuous reset method for discharging the leakage current and the signal charge in semiconductor radiation detectors with on-chip electronics has been studied and experimentally verified. The charge collected at the output electrode of the detector is discharged by means of the gate-to-drain current of the front-end JFET integrated in the detector itself. The suitable value of gate current is reached by means of a 'weak' avalanche breakdown mechanism which occurs in a high-field region of the transistor channel. When the JFET is operated in a source follower configuration, this mechanism is self-adapting to new values of leakage or signal currents. Index Terms - JFET's, silicon radiation detectors.

We present the first experimental characterization of an innovative two-chip detector system for X-ray spectroscopy experiments in which stability of operation is mandatory to avoid on-line calibration procedures. The system is based on a silicon drift detector and on a charge amplifier partly integrated in the detector chip. The design guidelines of both the 'detector chip' produced on a high resistivity substrate and the 'amplifier chip' designed in 0.8.[micro]m BiCMOS technology are reviewed. The proper functionality of each of the two chips and the performance of the whole system have been experimentally verified. Index Terms--Charge amplifier, high stability, X-ray spectroscopy.

A diode irradiation with 10-MeV protons was performed to measure the silicon current related damage rate at a temperature of -50°C. This measurement was fundamental to predict the performance of the detectors which will be used in the X-ray spectrometers of the Simbol-X and BepiColombo space missions. These detectors consist of arrays of large area silicon drift chambers with integrated depleted p-channel field effect transistors. The leakage current increase due to radiation damage and its consequent energy resolution degradation can be critical for these missions, specially for BepiColombo. These effects cannot be predicted because, during the whole missions, the sensors will be kept at temperatures below -40°C, and the existing models are based on measurements on structures which underwent annealing at higher temperatures. An irradiation experiment was performed to measure the current related damage rate at -50°C, and the obtained value was (11.1 ± 0.2) x 10-17 A/cm. This result implies that it will be possible to achieve the Simbol-X energy resolution, whereas some annealing strategies will be needed for the BepiColombo mission. The annealing behaviour at 60°C was studied as well and the results are in agreement with the already available measurements. [ABSTRACT FROM AUTHOR]