H. Videlier

Broadband terahertz imaging with highly sensitive silicon CMOS detectors

This paper investigates terahertz detectors fabricated in a low-cost 130 nm silicon CMOS technology. We show that the detectors consisting of a nMOS field effect transistor as rectifying element and an integrated bow-tie coupling antenna achieve a record responsivity above 5 kV/W and a noise equivalent power below 10 pW/Hz(0.5) in the important atmospheric window around 300 GHz and at room temperature. We demonstrate furthermore that the same detectors are efficient for imaging in a very wide frequency range from ~0.27 THz up to 1.05 THz. These results pave the way towards high sensitivity focal plane arrays in silicon for terahertz imaging.

A 280-GHz Schottky Diode Detector in 130-nm Digital CMOS

A 2×2 array of Schottky-barrier diode detectors with an on-chip patch antenna and a preamplifier is fabricated in a 130-nm logic CMOS process. Each detector cell can detect the 25-kHz modulated 280-GHz radiation signal with a measured responsivity and noise equivalent power (NEP) of 21kV/W and 360pW/ √Hz, respectively. At 4-MHz modulation frequency, NEP should be about 40pW/ √Hz. At supply voltage of 1.2V, the detector consumes 1.6mW. By utilizing the detector, a millimeter-wave image is constructed, demonstrating its potential application in millimeter-wave and THz imaging.

A broadband THz imager in a low-cost CMOS technology

Terahertz (THz) technology has become of large interest over the last 10 years. THz rays are an alternative to X-rays for imaging through thin materials and their non-ionizing character makes them inherently health-safe. The THz domain is also suitable for heterodyne detection and the use of radar techniques to perform 3D imaging. Commercial applications range from non-destructive testing, security screening of objects or persons, and medical imaging to secure communications.

Current driven resonant plasma wave detection of terahertz radiation: Toward the Dyakonov-Shur instability

The experiments on the dc current influence on resonant terahertz plasma wave detection in InGaAs∕InAlAs multichannel high electron mobility transistors are reported. We observed the line width shrinking when a dc current is applied. We show that this line width decrease is due to the current induced reduction of plasma wave damping and takes place because the current drives the system toward the Dyakonov-Shur plasma wave instability.

Oblique modes effect on terahertz plasma wave resonant detection in InGaAs/InAlAs multichannel transistors

We report on the demonstration of narrow terahertz plasma wave resonant detection at low temperature in 200nm gate length InGaAs∕InAlAs multichannel high electron mobility transistors. We observe that the resonant detection linewidth is smaller than in full channel high electron mobility transistors. We interpret this shrinking by the effect of multichannel geometry that does not allow oblique plasma mode propagation along the channel.

280-GHz schottky diode detector in 130-nm digital CMOS

A 2×2 array of 280-GHz Schottky-barrier diode detectors with an on-chip patch antenna (255 × 250 μm2) is fabricated in a 130-nm logic CMOS process. The series resistance of diode is minimized using poly-gate separation (PGS), and exhibits a cut-off frequency of 2 THz. Each detector unit can detect an incident carrier with 100-Hz ~ 2-MHz amplitude modulation. At 1-MHz modulation frequency, the estimated voltage responsivity and noise equivalent power (NEP) of the detector unit are 250 V/W and 33 pW/Hz1/2, respectively. An integrated low-noise amplifier further boosts the responsivity to 80 kV/W. At supply voltage of 1.2 V, the entire chip consumes 1.6 mW. The array occupies 1.5 × 0.8 mm2. A set of millimeter-wave images with a signal-noise ratio of 48 dB is formed using the detector. These suggest potential utility of Schottky diode detectors fabricated in CMOS for millimeter wave and sub-millimeter wave imaging.

Temperature enhancement of terahertz responsivity of plasma field effect transistors

Temperature dependence of THz detection by field effect transistors was investigated in a wide range of temperatures from 275 K down to 5 K. The important increase of the photoresponse following 1/T functional dependence was observed when cooling from room temperature down to 30 K. At the temperatures below ∼30 K, the THz response saturated and stayed temperature independent. Similar behavior was observed for GaAs, GaN, and Si based field effect transistors. The high temperature data were successfully interpreted using recent theory of overdamped plasma excitation in field effect transistors. The low temperature saturation of the photoresponse was tentatively explained by the change of the transport regime from diffusive to ballistic or traps governed one. Our results clearly show that THz detectors based on field effect transistors may improve their responsivity with lowering temperature but in the lowest temperatures (below ∼30 K) further improvement is hindered by the physics of the electron transport ...

Terahertz response of InGaAs field effect transistors in quantizing magnetic fields

Terahertz (THz) detection by plasma wave mechanism in InGaAs field effect transistors is studied in high/quantizing magnetic fields regime. The correlation between the photovoltaic response and magnetoresistance is revealed. It allows explaining the dominant physical mechanism responsible for strong oscillations observed in the transistor THz photoresponse. The results indicate also a serious discrepancy between experimental data and existing theoretical model.

Imaging above 1 THz limit with Si-MOSFET detectors

We demonstrate that a proper antenna and transistor design can provide high responsivity for Terahertz radiation and imaging capability even above the 1 THz limit with a low-cost 130 nm CMOS technology. This result opens the way to CMOS THz imagers working at high frequencies and therefore exhibiting high a spatial resolution — down to ~300 µm.

Field effect transistors for terahertz detection - silicon versus III–V material issue

Resonant frequencies of the two-dimensional plasma in FETs reach the THz range for nanometer transistor channels. Non-linear properties of the electron plasma are responsible for detection of THz radiation with FETs. Resonant excitation of plasma waves with sub-THz and THz radiation was demonstrated for short gate transistors at cryogenic temperatures. At room temperature, plasma oscillations are usually over-damped, but the FETs can still operate as efficient broadband THz detectors. The paper presents the main theoretical and experimental results on detection with FETs stressing their possible THz imaging applications. We discuss advantages and disadvantages of application of III–V GaAs and GaN HEMTs and silicon MOSFETs.