32-Channel 80 dB Dynamic Range Direct-Injection Current-Integrating ROIC for Ge-on-Si Detectors in a Near-Infrared Microspectrometer

In this letter, we propose a 32-channel direct-injection current-integrating readout integrated circuit (ROIC) for novel near-infrared microspectrometers based on backside-illuminated Germanium-on-Silicon (Ge-on-Si) near-infrared detectors. The ROIC provides near-zero-volt biasing to the Ge-on-Si detectors to keep them operating in the lowest dark current zone for the best signal-to-noise ratio. By choosing a proper integration time, a wide dynamic range of photocurrents can be processed. In our specific application, a microspectrometer with 80 dB photocurrent dynamic range, i.e., 5 pA to 50 nA, is targeted and successfully implemented. With this, the ROIC is one of the enabling parts to build up the novel backside-illuminated near-infrared microspectrometer. A test spectroscopy measurement on water and isopropanol has been carried out. Water, isopropanol, and their mixtures are clearly distinguishable, which delivers a good proof-of-concept of the ROIC and the overall microspectrometer design.