KEYWORDS: Photodiodes, CMOS technology, Standards development, Diffusion, Data modeling, Signal processing, Imaging systems, Palladium, Very large scale integration, Near field optics
This work shows the progress and demonstrates the measurements performed via a unique submicron scanning system developed at the VLSI systems center in Ben-Gurion University.
The system enables the combination of near-field optical and atomic force microscopy measurements with the standard electronic analysis. The obtained signal, i.e., the electrical outcome at each point as a function of the spot position provides a 2D signal map of the pixel response, representing the full 3D charge distribution in the device.
This work present the results obtained by thorough scanning of several various pixel topologies of CMOS APS chips fabricated in two different CMOS technologies (the standard 0.5μm and 0.35μm CMOS technologies).
We demonstrate that our system use enables a detailed, point by point, quantitative determination of the contributions to the total output signal from each particular region of the pixel. It makes possible to understand the influence of the each component composing the pixel (e.g., logic transistors, metal lines, etc.) which is extremely important for CMOS APS where the pixel structure defines a fill factor of less then 100%.
KEYWORDS: Photodiodes, Diffusion, Point spread functions, Imaging systems, Sensors, Modulation transfer functions, Process modeling, Silicon, Absorption, Active sensors
This paper presents the pioneer use of our unique Sub-micron Scanning System (SSS) for point spread function (PSF) and crosstalk (CTK) measurements of focal plane CMOS Active Pixel Sensor (APS) arrays. The system enables the combination of near-field optical and atomic force microscopy measurements with the standard electronic analysis. This SSS enables full PSF extraction for imagers via sub-micron spot light stimulation. This is unique to our system. Other systems provide Modulation Transfer Function (MTF) measurements, and cannot acquire the true PSF, therefore limiting the evaluation of the sensor and its performance grading. A full PSF is required for better knowledge of the sensor and its specific faults, and for research - to enable better optimization of pixel design and imager performance.
In this work based on the thorough scanning of different “L” shaped active area pixel designs (the responsivity variation measurements on a subpixel scale) the full PSF was obtained and the crosstalk distributions of the different APS arrays are calculated. The obtained PSF points out the pronounced asymmetry of the diffusion within the array, mostly caused by the certain pixel architecture and the pixels arrangement within the array. We show that a reliable estimate of the CTK in the imager is possible; the PSF use for the CTK measurements enables not only its magnitude determination (that can be done by regular optical measurements), but also to discover its main causes, enabling the design optimization per each potential pixel application.
This work presents an empirical dark current model for CMOS Active Pixel Sensors (APS). The model is based on experimental data taken of a 256 X 256 APS chip fabricated via HP in a standard 0.5 micrometers CMOS technology process. This quantitative model determines the pixel dark current dependence on two contributing factors: the 'ideal' dark current determined by the photodiode junction, introduced here as a stable shot noise influence of the device active area, and a leakage current due to the device active area shape, i.e., the number of corners present in the photodiode and their angles. This part is introduced as a process induced structure stress effect.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.