Pixel readout IC for CdTe detectors operating in single photon counting mode with interpixel communication

This paper presents a readout integrated circuit (IC) of pixel architecture called MPIX (Multithreshold PIXels), designed for CdTe pixel detectors used in X-ray imaging applications. The MPIX IC area is 9.6 mm × 20.3 mm and it is designed in a CMOS 130 nm process. The IC core is a matrix of 96 × 192 square-shaped pixels of 100 µm pitch. Each pixel contains a fast analog front-end followed by four independently working discriminators and four 12-bit ripple counters. Such pixel architecture allows photon processing one by one and selecting the X-ray photons according to their energy (X-ray colour imaging). To fit the different range of applications the MPIX IC has 8 possible different gain settings, and it can process the X-ray photons of energy up to 154 keV. The MPIX chip is bump-bonded to the CdTe 1.5 mm thick pixel sensor with a pixel pitch of 100 µm. To deal with the charge sharing effect coming from a thick semiconductor pixel sensor, multithreshold pattern recognition algorithm is implemented in the readout IC. The implemented algorithm operates both in the analog domain (to recover the total charge spread between neighboring pixels, when a single X-ray photon hits the border of the pixel) and in the digital domain (to allocate a hit position to a single pixel).

Readout Integrated Circuit for Small-Sized and Low-Power Gas Sensor Based on HEMT Device

This paper presents a small-sized, low-power gas sensor system combining a high-electron-mobility transistor (HEMT) device and readout integrated circuit (ROIC). Using a semiconductor-based HEMT as a gas-sensing device, it is possible to secure high sensitivity, reduced complexity, low power, and small size of the ROIC sensor system. Unlike existing gas sensors comprising only HEMT elements, the proposed sensor system has both an ROIC and a digital controller and can control sensor operation through a simple calibration process with digital signal processing while maintaining constant performance despite variations. The ROIC mainly consists of a transimpedance amplifier (TIA), a negative-voltage generator, and an analog-to-digital converter (ADC) and is designed to match a minimum target detection unit of 1 ppm for hydrogen. The prototype ROIC for the HEMT presented herein was implemented in a 0.18 µm complementary metal–oxide–semiconductor (CMOS) process. The total measured power consumption and detection unit of the proposed ROIC for hydrogen gas were 3.1 mW and 2.6 ppm, respectively.

A High-resolution Colloidal Quantum Dot Imager by Monolithic Integration

Near-infrared (NIR, 0.7–1.4 µm) imagers have wide applications in night surveillance, material sorting, machine vision and potentially automatic driving. However, limited by the high-temperature processing and requirement of single-crystalline substrate, so far flip-chip is the dominant way to connect infrared photodiodes and silicon-based readout integrated circuit (ROIC) to produce infrared imagers, suffering from complicated process and ultra-high cost and hence limiting their widespread applications in the market. Here we report the monolithic integration of colloidal quantum dots (CQD) photodiodes with complementary metal-oxide-semiconductor (CMOS) ROIC, operating as a low-cost and high-performance imager. The CQD photodetector is well designed with a CMOS-compatible structure, demonstrating a response spectral range of 400–1300 nm, a detectivity of 2.1×1012 Jones at room temperature, a -3dB bandwidth of 140 kHz and a linear dynamic range over 100 dB. The CQD imager can identify materials, inspect apple scar and veins with a large size of 640×512 pixels and a spatial resolution of 40 lp/mm at a modulation transfer function of 50%. Monolithic integration significantly reduces the cost without sacrificing performance, thus providing huge potential for the ubiquitous deployment of infrared imagers.