TAILIEUCHUNG - Photodiodes World Activities in 2011 Part 5

Tham khảo tài liệu 'photodiodes world activities in 2011 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Image Artifacts by Charge Pocket in Floating Diffusion Region on CMOS Image Sensors 111 a d b c Fig. 11. The region of photo diode pass transistor and floating diffusion for four-transistor type active pixel. a Layout. b Tape-A Cross sectional view for diode on line AB region c Type-B Cross sectional view for diode on line CD region. d Concept for test pattern to measure the pinch off voltage. Source direct frontside and drain direct backside on b and c . Also gate connected with p-sub. In order to confirm the changing of the doping profile pinch off voltage is measured in JFET junction field effect transistor structure as shown in Fig. 12 a . Pinch off is defined as a voltage when junction is fully depleted by applying reverse voltage at the p-layer and p-sub region. Here pinch off voltage can be defined the ratio of n- and p-type doping concentration. Doping profile with FD regions can be easily analyzed by using the JFET structure. Dependences of process and test pattern are analyzed to understand doping profile by measuring pinch off voltage. Fig. 12 b shows the pinch off voltage for gate polybounded FD type-A and STI-bounded FD type-B as a function of test patterns for process-1 and -2. Gate poly-bounded FD Type-A shows the different pinch off voltage with process-1 and process-2. Clearly the increase of pinch off voltage in process-2 leads to the changing of doping profile under sidewall spacer in gate poly-bounded FD type-A which could explain the electric field improved in the sidewall spacer overlap region. But STI-bounded FD type-B shows similar pinch off voltage without processes which means pn diode controlled to the same dose. For the test pattern types gate poly-bounded FD type-A with sidewall spacer overlap has higher pinch off voltage than that of STI-bounded FD type-B . This means that pattern geometric can be effected the difference of pinch off voltage during biasing. From these results it is observed that process-2 has lower n-type doping .

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