Every software package contains a full set of examples suitable for that version and are installed with the software. If you see examples here that are not in your installation you should consider updating to a later version of the software. These examples can be used by beginners and advanced users for product evaluation, teaching purposes, and self-training.
Required Modules
Victory Process
- 2D Diffusion & Implantation
Victory Mesh
- 2D Meshing
Victory Device
- 2D Simulator
- 2D Optical
This example demonstrates Process and Device simulation of a PPD (Pinned Photo Diode) CMOS Image sensor. Front end as well as back-end process simulation including lens are performed using Victory Process, remeshed in Victory Mesh, and Device simulation is performed using Victory Device. Illumination is performed using 530nm wavelength light source with exposure time for 100 e-6 seconds and 0.001 W/cm3 intensity. Both exposure time and beam intensity are set as variables so they can be changed without changing the rest of the device flow.
PPD CMOS image sensor is a special transistor where the source region is the floating N- region underneath a heavy P+ doping pin layer. This N-well is called the PPD (Pinned Photo Diode) well. When light illuminates this PPD well, large quantity of electrons is generated due photoelectric effect. The amount of charge generated depends on the wavelength of incident light and time of exposure.
The device simulation is set up in 4 sections. All sections can be run independently or the entire example can be run in a single go:
Section 1: performs DC saturation IV characteristics to obtain the transfer gate channel’s threshold voltage (Vth). This is value of gate voltage at which isolated PPD well is connected to transfer gate via an inversion channel. During image sensor operation, this would be the turn on voltage during charge transfer. Since the PPD well is floating, instead of electrode in PPD well, PROBE is used to track the potential and electron concentration of a point in the channel region which is used to obtain the IV characteristics.
Section 2: extracts Pinning Voltage and equilibrium full-well capacity (EFWC) of the image sensor. Pinning voltage (Vpin) is calculated as the maximum variation of electrostatic potential in the PPD well, i.e., deviation of the conduction band from equilibrium ( solve prev ) to full well depletion state i.e., Vd=3.3 & Vg=3.3. Equilibrium full well capacity (EFWC) is calculated as the total electron concentration in the PPD well at equilibrium state, i.e., just after solve prev when all electrodes are at 0V.
Section 3: Simulates dark and light current from the image sensor.
Section 4: Simulates complete device behaviour in transient mode. Operation flow includes isolation of PPD well (VD=3.3V, Vg=3.3 -> Vg=0V), illumination of PPD well using 530 nm light source and 0.001 W/cm3 intensity, floating diffusion drain, and transfer accumulated charge through transfer gate. Ray tracing is used in this case, but FDTD can also be used. For a more detailed description of FDTD syntax please refer to image sensor examples 1 to 3. The example also calculates Charge Transfer Efficiency of the designed PPD Image sensor at the end.
Images
