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The response curve as a function of different exposure times. Here the buried photodiode parameters are the same as those in Figure 2; the exposure times are set at 40 ms, 20 ms, 10 ms, and 5 ms, respectively (in order from left to right).
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In this paper, we present a new logarithmic pixel design currently under development at New Imaging Technologies SA (NIT). This new logarithmic pixel design uses charge domain logarithmic signal compression and charge-transfer-based signal readout. This structure gives a linear response in low light conditions and logarithmic response in high light...
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This study proposes vertical sidewall implantation for noise reduction of CMOS image sensor pixel employing a vertical transfer gate (VTG). The pixel performance is evaluated by 3D device-level simulation. It is concluded that the proposed pixel's output is less sensitive to interface traps compared to similar previous work. In previous back-side-i...
Citations
This article discusses approaches for expanding the dynamic range of measuring systems by implementing phase triangulation methods and structured illumination. These systems are designed for the high-precision measurement of the geometric parameters of complex profile products with arbitrary light-scattering surface properties. A method for expanding the dynamic range of thea measuring system is proposed, which is based on the automatic adjustment of the photodetector exposure duration, redundant collection of experimental data, and complex regression analysis. The results of experimental studies on the efficiency of the proposed method are presented. It has been demonstrated that the classical approach to interpreting images obtained using a photodetector with a fixed exposure duration almost always causes a large measurement error in the geometric parameters of a surface with a wide range of light-scattering properties. At low exposure values, the error in measuring the geometric parameters of the surface increases in the dark area, where the signal level is substantially weaker compared to the light areas of the measured surface. At high exposure values, the error in measuring the geometric parameters of the light area of the surface increases because the signal is outside the dynamic range of the photodetector. For the measured geometric parameters of surfaces with different light-scattering properties, the use of a photodetector with an extended range enables achieving a measurement error less than or approximately equal to the error of a measuring system containing a photodetector with a fixed exposure. Expanding the dynamic range simplifies automated measurements because there is no need to further optimize the photodetector parameters for the light-scattering properties of the surface of the measured object.
The article is devoted to the development of phase triangulation and structured illumination methods for measuring the geometry of objects with arbitrary light-scattering surface properties. A method for expanding the dynamic range of a measuring system that implements the phase triangulation method is proposed. The method is based on automatic adjustment of the exposure time of the photodetector, excessive collection of experimental data, and complex regression analysis. The results of experimental studies of the effectiveness of the proposed method for expanding the dynamic range of the measuring system are presented. It is shown that the classical approach to image interpretation using a photodetector with a fi xed exposure duration almost always leads to a high level of error over the entire range of light-scattering properties of the surface. For low exposure values, there is an increase in the measurement error in the region of the dark surface, since the signal level there turns out to be signifi cantly weaker than for the bright regions of the measured surface. For large exposure values, an increase in the error is observed when measuring the bright area of the measured surface, since the signal is outside the dynamic range of the photodetector. The proposed method of image interpretation with an extended range of the measuring system demonstrates an error level less than or comparable to the results of image interpretation with a fi xed exposure for all measured light-scattering properties of the surface.
The proposed method makes it possible to perform automated measurements without additional optimization of the photodetector parameters for the light-scattering properties of the surface of the measured object.
This brief presents offset and gain FPN calibrated linear-logarithmic image sensor. Offset FPN originated from threshold voltage variation of the logarithmic conversion transistor is calibrated with Two-step charge transfer operation. Remaining gain FPN is analyzed and its root cause is investigated. The subthreshold slope difference of the logarithmic conversion transistors in the shared pixel architecture is found to be responsible for the increasing FPN in the logarithmic operation region and potentially limiting dynamic range in high illumination region. A simple modeling-based gain FPN correction method in linear-logarithmic APS using shared pixel architecture has been proposed. The prototype sensor is fabricated by using a 0.13-
$\mu \text{m}$
CMOS image sensor process. Thanks to the proposed gain FPN correction together with offset correction using Two-step charge transfer operation, wide dynamic range of more than 120 dB has been achieved while maintaining the total FPN less than 0.29% over the entire dynamic range.
A new type of light sensor called FDPix, composed of one transistor (1T) per pixel is investigated. It consists in co-integrating an FDSOI (Fully-Depleted Silicon-On-Insulator) transistor with a photodiode to enable light sensing through optical back biasing. The absorption of photons and resulting photogenerated charges in the diode will result in a Light Induced VT Shift (LIVS). The LIVS is due to a capacitive coupling between the front and back gate of the FDSOI transistor and represents the key performance metric to be extracted and optimized. In this work, the device behavior in dc and transient domains was thoroughly investigated and modeled. Although not limited to this node, all the devices tested were fabricated using 28nm node FDSOI technology. By means of TCAD simulations and opto-electrical characterization, the device parameters such as Body Factor (BF) and junction profile were optimized to improve its performance. It was found that the FDPix is in fact a dual response sensor. It exhibits a linear response at low light intensity which results in high sensitivity, and a logarithmic response at higher intensities that ensures a high dynamic range (DR) of more than 120dB. The dedicated developed model is implemented in SPICE environment for circuit design. New pixel circuit in analog and digital domain, based on the FDPix were designed, fabricated, and tested. The results obtained and presented in this work, shows the potential of using the FDPix sensor for smart, highly embedded, low power image sensors for More-than-Moore applications.
This paper presents the study of a monolithically integrated FDSOI-based pixel sensor, called FDPix. The FDPix consists in cointegrating a photodiode in the substrate of an fully depleted silicon on insulator (FDSOI) transistor. Its principle of operation is based on optical back biasing of FDSOI transistor characteristics under photodiode illumination. A reset mechanism is demonstrated using the back gate of the transistor and can be applied commonly to all pixels, allowing a very small footprint. The investigation is carried out by means of TCAD simulation, analytical modeling, and optoelectrical characterization to evaluate the sensor's characteristics and to optimize the device technological parameters. The pixel exhibits two responses, linear response at low intensities and logarithmic response at high intensities, achieving a high dynamic range (DR) of 120-130 dB.
