Low noise photon-counting pixel detectors

The response to the test charge-pulses of known values. The noise has been measured by fitting of Gaussian functions. The noise floor is about 2e. The additional signal-dependent noise nearly depends as the square root of the number of electrons in the input signal.
An interesting effect has been measured at lower temperatures (-10C to -30C). The output pulse amplitude has been measured using the time-over-threshold method. The left peak is the noise peak; the right peak is the response to 9e test pulses. The histogram of the noise peak contains several pronounced peaks - certain discrete amplitude values occur more often.
The histogram of the noise peak. Certain discrete amplitude values occur more often.


Bioquant1 and 2 are two detectors with the aim to demonstrate the limits in the low-noise operation in 180nm UMS technology. The detector is a small diffusion diode that is readout by a high gain charge sensitive amplifier. We have implemented several pixels with different diode geometries and types. Our goal is to achieve the sub-electron noise that could allow the detection of single photons in visible energy range without the need for avalanche signal multiplication. Possible application is the detection of fluorescence light in biology-research (cell- and gene-studies).


We have measured the response to the capacitive test signals and to the LED light pulses. Careful calibration has been performed using test diodes and by comparing the measurement- and the simulation results. We measure a noise of 2e (sigma value) at room temperature. The noise should scale down with the transistors- and the diode-size and their capacitances. We are hoping to achieve better results with in a more advanced technology. Interesting effects have been observed at lower temperatures.

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