The spread of practical terahertz (THz) systems dedicated to the telecommunication, pharmacy, civil security, or medical markets requires the use of mainstream semiconductor technologies, such as complementary metal-oxide-semiconductor (CMOS) lines. In this paper, we discuss the operation of a CMOS-based free space all-electronic system operating near 250 GHz, exhibiting signal-to-noise ratio (SNR) with 62 dB in the direct detection regime for one Hz equivalent noise bandwidth. It combines the state-of-the-art detector based on CMOS field-effect-transistors (FET) and a harmonic voltage-controlled oscillator (VCO). Three generations of the oscillator circuit are presented, and the performance characterization techniques and their improvement are explained in detail. The manuscript presents different emitter–detector pair operation modalities, including spectroscopy and imaging.

We studied time resolution and response power dependence of three terahertz detectors based on significantly different types of field effect transistors. We analyzed the photoresponse of custom-made Si junctionless FETs, Si MOSFETs and GaAs-based high electron mobility transistors detectors. Applying monochromatic radiation of high power, pulsed, line-tunable molecular THz laser, which operated at frequencies in the range from 0.6-3.3 THz, we demonstrated that all these detectors have at least nanosecond response time. We showed that detectors yield a linear response in a wide range of radiation power. At high powers the response saturates varying with radiation power P as U = R0P/(1 + P/Ps), where R0 is the low power responsivity, Ps is the saturation power. We demonstrated that the linear part response decreases with radiation frequency increase as R0 ∝ f −3 , whereas the power at which signal saturates increases as Ps ∝ f 3 . We discussed the observed dependences in the framework of the Dyakonov-Shur mechanism and detector-antenna impedance matching. Our study showed that FET transistors can be used as ultrafast room temperature detectors of THz radiation and that their dynamic range extends over many orders of magnitude of power of incoming THz radiation. Therefore, when embedded with current driven read out electronics they are very well adopted for operation with high power pulsed sources.PACS numbers:

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This work presents the integrated, multichannel readout circuit dedicated to FET-based THz detectors. Described solution provides an unique approach to FET detectors readout, able to replace the measurement equipment deploying the lockin technique and to eliminate the necessity of modulating the THz wave. The IC proposed by the authors is based on the chopper amplifier architecture, enhanced and adapted for multichannel signal processing. It also ensures significant 1/ f noise minimisation, which is the key requirement for the FET-based detectors readout. The circuit prototypes were manufactured in standard 350 nm CMOS process (AMS A.G.) and then measured in the dedicated test set-up.

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