Application of HEMT for multiplexing large arrays of high impedance LTDs

The development of large arrays of detectors requires using a proximate electronics at low temperatures for signal multiplexing and amplification. We report the use of commercial High Electronic Mobility Transistors (HEMT) for multiplexing signals from high impedance LTD arrays (typ. 10–100 MΩ). The electronic architecture is based on HEMTs cooled at 0.1 K for the multiplexer and a JFET amplifier cooled at 100 K with <1 nV/Hz1/2 noise figure. For this time-multiplexing scheme, a capacitor is used to integrate the signal between measurements. Two main solutions are compared for the detectors polarization: the first uses a classical resistive method; the second uses a common capacitor allowing to polarize the detectors individually. The multiplexing ratio is mainly limited by the amplifier noise to about 20 detectors per amplifier with a pixel sampling rate of about 60 Hz. A specific development of HEMT arrays with Quantum Point Contacts (QPC-HEMT) with very small grid-to-channel capacitor (∼1 fF) allows minimizing the transient effects and realizing a close integration with the LTD arrays.