Technology trend in real-time, uncooled image sensors for sub-THz and THz wave detection

Abstract

The author summarizes development of uncooled microbolometer terahertz (THz) focal plane arrays (FPAs) and real-time cameras for sub-THz and THz wave detection. The array formats are 320x240 and 640x480, and the cameras have several functions, such as lock-in imaging, external-trigger imaging, image processing (pixel binning and frame integration), beam profiling and so on. The FPAs themselves are sensitive to sub-THz, THz and infrared radiations.Active imaging systems based on the imagers are described. One of them is a real-time transmission-type THz microscope which contains a THz camera and a quantum cascade laser (QCL). The other one is an active sub-THz imaging system, where a transmission imaging mode and a reflection imaging mode can be switched with one-touch operation. Strong THz emitters, such as far-infrared gas lasers and QCLs, are strongly coherent and often produce interference fringes in an image. A method of reducing the interference fringes (beam homogenizing) is described.Microbolometer FPAs developed by other groups, antenna-coupled CMOS FPA, array detectors based on GaAs high-mobility heterostructure and so on are also summarized, which operate in real-time and at room temperature. A fair method of evaluating performance of detectors with different sizes and at different wavelengths is explained and the performances of the detectors are compared.

Roadmap of Terahertz Imaging 2021

“…Recent advances: As important other members in the family of room temperature THz sensors, one can mention diode structure-based devices and microbolometers [167]. As a classical example of diodes, one can underline Schottky diodes, which have already long been and continue to be one of the most useful THz devices both in detection and THz emission schemes as high as 3 THz frequencies [87].…”

“…The considered devices are plotted with respect to the emitting power in sources section (left) and the noise equivalent power (NEP) in sensors one (right). Taken data references: Schottky diodes multipliers[87,439] CMOS-based and SiGe-based electronic emitters[62]; CMOS and SiGe detectors parameters[159], parameters of Schottky detectors [440], microbolometers values[167], conventional THz QCL[41]; frequency-difference THz QCLs (FD THz QCLs) parameters-from publications by M. Razeghi[51,52] and M. Belkin's[53] groups. Optoelectronic THz systems (denoted as red solid lines) are attributed for the emitters section only.…”

Towards Practical Terahertz Imaging System With Compact Continuous Wave Transceiver

“…As it is discussed in Section II. A, although integrated transceiver array systems are limited at the 300-GHz band, THz detector arrays, which are also defined as THz cameras, are based on relatively mature techniques [7], [45], [62], [79]. Owing to the high cost and limitation of the directional THz beam, the current devices can only image a small area, hence the combination of a linear array with a quasi-optic system is also an effective way to further enhance the imaging speed while achieving a larger survey area [37], [45], [79].…”

Field-Effect Transistor Based Detectors for Power Monitoring of THz Quantum Cascade Lasers

“…Due to required biasing, these devices exhibit strong 1/f noise contribution; thus, the listed performance is achievable only in the shot-noise-limited regime for modulation frequencies typically exceeding 100 kHz. The successful demonstration of the operation of a standard infrared imager at 4.3 THz with a NEP value of 320 pW/ √ Hz [36] launched the race between the manufacturers of microbolometer (μ Bolometer) cameras, and now, THz-tailored devices demonstrate unprecedented NEP values below 10 pW/ √ Hz [27], [29]. One drawback of microbolometers could be their considerably long integration time, which is close to the inverse of the frame rate [27].…”

“…The successful demonstration of the operation of a standard infrared imager at 4.3 THz with a NEP value of 320 pW/ √ Hz [36] launched the race between the manufacturers of microbolometer (μ Bolometer) cameras, and now, THz-tailored devices demonstrate unprecedented NEP values below 10 pW/ √ Hz [27], [29]. One drawback of microbolometers could be their considerably long integration time, which is close to the inverse of the frame rate [27]. There are reports that single devices can have submicrosecond thermal response times [37]; these data are available only for devices optimized for 300 and 765 GHz.…”