AVS 57th International Symposium & Exhibition
    MEMS and NEMS Thursday Sessions
       Session MN-ThP

Paper MN-ThP9
Development of Optimum Ti/TiN Dark Reference Structure to Improve Dark Leakage Characteristics in CMOS Image Sensor

Thursday, October 21, 2010, 6:00 pm, Room Southwest Exhibit Hall

Session: MEMS and NEMS Poster Session
Presenter: N.-H. Kim, Chonnam National University, Republic of Korea
Authors: S.-Y. Kim, Korea Polytechnic College IV, Republic of Korea
N.-H. Kim, Chonnam National University, Republic of Korea
K.-G. Oh, Chosun University, Republic of Korea
Correspondent: Click to Email
Dark leakage is one the most effective factors influencing the characteristics of CMOS image sensor (CIS), which makes the unrelated signals instead of the when the low intensity of illumination lighted up to image sensors. To solve this problem, there are so many efforts into changing the designs and fabrication processes. One of these efforts is the usage of dark reference to improve the dark leakage characteristics. In this study, the CIS including dark reference was fabricated. The dark reference located in the edge of the valid pixel makes no sigmal from light through perfectly blocking out light, which is used to by using the metal thin films. For easy fabrication and excellent stability, Ti/TiN structure was employed in this experiment. The dark reference by Ti/TiN structure showed the lower leakage characteristics the under-lying photodiode than that of the valid pixel in the general H2 annealing time (30 min). The dark leakage characteristics were improved by increasing the H2 annealing time; however, the increased annealing time lead the fabrication ability and yield to be lower. Therefore, the optimized thickness (150 nm) of Ti/TiN structure were obtained by theoritical estimation for the under 0.01% transmittance. In experiment, the leakage characteristics were improved in the conventional H2 annealing time by decreasing the thickness of Ti in Ti/TiN structure. Consequently, the dark leakage characteristics and SNR of CIS were improved by optimization of Ti/TiN thickness with the short fabrication/annealing time.