Image Sensor Cell including 2 Pass Transistors

imagesensorex06.in : Image Sensor Cell including 2 Pass Transistors

Requires: Victory Process, Victory Mesh, Victory Device
Minimum Versions: Victory Process 7.30.4.R, Victory Mesh 1.4.6.R, Victory Device 1.14.1.R

By default Victory Process and Device run on just one processor. To ensure better perfomance on your computer the following simulation condition simflags="-P all" could be specidied in the go line starting Victory Process or Device. This means that all processors available will be used. If you want to use a smaller number of processors you can substitute "all" with a desired number, e.g. simflags="-P 4".

This examples demonstrates solutions to some of the particular 3D process and device issues when simulating a 3D image sensor cell. The first issue with a number of designs is the very high implantation energies required to isolate the active region of the image sensor.

If 3D Monte-Carlo Implantation is used to simulate these high energy implants, the simulation times can be excessive. The solution is to simulate these implants as a single spot in Athena and then to extract the depth and lateral spreading of the implants using deckbuild's extract statements. This creates an accurate data file of the implant, which can then be imported into Victory cell using the profile statement and incorporated into the 3D structure when required using the implant statement.

The device simulation is in three parts. Firstly the threshold voltage of the two pass transistors is simulated. Then a dark transient is simulated to find the dark current recovery time, which sets the low light sensitivity limit of the image sensor, ie the maximum useable light integration time. Finally a simulastion is done illuminating the device with a typical average light intensity of 0.01 Watts/cm2 with a standard solar AM 1.5 spectrum, which for this sesnor, would require an integration time of approximately 0.0008 for a 50% exposure level. The illumination intensity and exposure integration time can both be adjusted by changing these two variable quantities at the set statement lines, near the top of the inpu file for the final device simulation.

The threshold voltage of the pass transistors is deliberately high to ensure that charge leakage in their off state is minimized. Since the pass transisotrs have a common floating electrode without an ohmic contact, the threshold voltage is plotted using the electron concentration under the gates. The electron concentrations are measwured using probe statemnts, which probe the silicon surface under the gates. In this example, the probe quantities have been called "cg_conc" and "ng_conc" .

For the transient simulations, the output voltage of the cell can be monitored in tonyplot by plotting the probe quantity called fd_potential . Another interesting quantity also extracted using the probe statement is the electron concentration in the active image sensor region. This image sensor electron concentration is called "cis_conc" in this example.

To load and run this example, select the Load button in DeckBuild > Examples. This will copy the input file and any support files to your current working directory. Select the Run button in DeckBuild to execute the example.