[Paper] A High Quantum Efficiency High Readout Speed 1024 Pixel Ultraviolet-Visible-Near Infrared Waveband Photodiode Array

Abstract

Spectrometers are widely used in the various fields of scientific analyses, life science, environmental assessment, food inspection and so on 1)~3). High sensitivity for UV-VIS-NIR light waveband is strongly required for PDA used in spectrometers to analyze various measurement samples accurately. In addition, a high readout speed performance is beneficial to improve the measurement throughput. Furthermore, high stabilities of light sensitivity and dark current of PDA toward UV-light irradiation are required for a long time use of the spectrometers without complicated maintenance. The quantum efficiency (QE) of a light detector is determined by the product of light transmittance to the photoelectric conversion part of PD and the efficiency to collect photo-generated carriers. In recent years, a Si photodiode junction technology to achieve high incident light sensitivity and high stability toward UV-light using a surface high concentration layer with steep dopant concentration profile formed on flattened Si surface has been developed, and single PD, PDA and area CMOS image sensors using the developed technology have been reported to exhibit superior characteristics 4)~9). Fig.1 shows the schematic image of a spectrometry system with a diffraction grating and a PDA as spectral light detector. Spectral light is irradiated to the pre-designated positions of the PDA. For general PDAs, the dielectric film above the PD is uniformly formed across the whole light receiving surface, thus, it is difficult to optimize the transmittance for all of the receiving light waveband. Meanwhile, image sensors with Fabry-Perot spectral filters directly formed on the top surface of monochrome CMOS image sensors have been reported to be useful to form hyperspectral line scan imagers 10). The reported Abstract A high QE and high readout speed ultraviolet-visible-near infrared (UV-VIS-NIR) light waveband linear photodiode array (PDA) is demonstrated in this paper. For the developed 1024 pixel PDA with the pixel size of 25 µm H × 2500 µm V , seven types of high transmittance optical layers were introduced for multiply divided pixel groups to achieve high QE for receiving light waveband and multiple transfer gates were placed along the long side of PD to improve readout speed. The fabricated PDA exhibited an average QE of 70 % for 200-800 nm and 80 % for 200-320 nm wavebands, the full well capacity (FWC) of over 70 pC and the line scan period of 0.33 msec simultaneously. The condition of top surface dopant concentration of the surface p + layer of photodiode (PD) to prevent sensitivity degradation due to deuterium lamp irradiation was also clarified.

[Invited Paper] A High SNR Global Shutter CMOS Image Sensor Technology for High Precision Absorption Imaging Applications

“…Here, calculation with α of 3 ensures 99.7 % detection accuracy. Approximately 70 dB SNR is required to detect absorption as small as several tens to several hundreds of ppm, which is comparable to stand-alone detectors 4) . Noise of image sensor can be classified into photon shot noise and dark noise and SNR of image sensor is given by equation (3), where, N sig is number of signal electrons, ndark is number of input referred dark random noise electrons consisting of ninput and σread/CG.…”

A 70-dB SNR High-Speed Global Shutter CMOS Image Sensor for in Situ Fluid Concentration Distribution Measurements

“…Several concentration measurement methods using light absorption have been utilized in high-performance liquid chromatography with linear array sensor [3], [4], gas concentration sensor with a single photodiode (PD) [5], and so on. Equation (1) where N sig is the number of signal electrons and n sys is the number of input-referred system noise electrons.…”