Title: A NEW METHOD TO ESTIMATE THE SENSITIVITY OF A PHOTO-TRANSISTOR IN AN IMAGE SENSOR

Year of Publication: Jul - 2013
Page Numbers: 99-103
Authors: Sangsik Park, Hyungsoo Uh
Conference Name: The Third International Conference on Digital Information and Communication Technology and its Applications (DICTAP2013)
- Czech Republic

Abstract:


A new method to predict the sensitivity of a photo transistor used in a pixel of an image sensor is proposed. The sensitivity of an image sensor should be measured after the assembly process. The prediction of the sensitivity before the package is very useful in the manufacturing of the image sensor. The doping of the base layer of the photo transistor affects the current gain and the breakdown voltage simultaneously. Therefore the breakdown voltage can reflect the gain of the transistor. That means the amplified photo current can be predicted by measuring the breakdown voltage. The signal is amplified by the operation of the bipolar transistor in the pixel in the operation of an optical mouse sensor. A method to predict the amplified photo current is required to reflect that in the mass-production since the current gain of the bipolar transistor is varied by the various mechanisms.. In this paper, we propose a simple method to predict the photo-current by measuring the breakdown voltage of the bipolar transistor in the test pattern. The analysis of the experiments showed that the trend of the breakdown voltage coincide exactly with that of the photo current. The image sensor using this new proposal about the estimation of the sensitivity by measuring the breakdown voltage was fabricated using the standard CMOS process. The performance of this new proposal was proved in the image sensor of an optical mouse.