# Presentation: 432251

## Simulation Of The Electrostatic Field Distribution In A Pixel Device (update)

- Marina, Artuso
- Chaouki, Boulahouache
- Phys. Dept.
- Syracuse University

## Goals Of The Simulation

- Determination of the electrostatic field properties of a pixel device in both p-stop and p-spray configuration.
- Assess radiation damage before and after irradiation such that we,
- Optimize the pixel structure so that the lateral field is minimized(to avoid impact ionization and avalanche break down).
- Get a feeling how the surface charge density does affect both isolations.
- Determine the efficiency of charge collection and dynamical properties influencing charge sharing.

- Chaouki, Boulahouache

- January 22, 2001

## Outline...

- Things to be discussed in this presentation,
- The field distribution for p-stop and p-spray pixels before & after irradiation.
- The comparison between lateral field distributions in both cases.
- The surface charge density dependence of the electric field of p-spray isolation technique, and a qualitative comparison with results obtained from an article titled,
- “HERA-B Detectors With P-spray Isolation On The N-side” done by Kari S. H., Trond W. and Berit S. A.

- Chaouki, Boulahouache

- January 22, 2001

## Brief Description Of The Processors Used

- Chaouki, Boulahouache

- January 22, 2001

## The Geometry...

- A simplified geometry has been adopted.

- Chaouki, Boulahouache

- January 22, 2001

## Grid size...

- A finite element analysis requires a grid size input, we have adopted the following:

- For the height,
-  Maximum height = 0.24m
-  Minimum height = 0.12m

- For the width,
-  Maximum width = 0.24m
-  Minimum width = 0.12m

-   and this is over a region of 100 m of width and 9 m of depth.

- Chaouki, Boulahouache

- January 22, 2001

## P-stop And P-spray Pixels

- We will study the P-stop and P-spray pixels where the basic structure is the same except that the doping distribution differs. We used a depth of 1.75m for P-stop pixels(as obtained from SINTEF measurement.), and 1m for P-spray pixels.
- An approximate structure to the graded p-spray will be investigated.

- Chaouki, Boulahouache

- January 22, 2001

## Surface charge density and Substrate...

- Before irradiation,
- The substrate is of an n-type with a 2e+12/cm-3 concentration.
- The surface charge density is about 3e+11 /cm-2 .
-  To model the irradiation effect we have to change the following parameters,
- The substrate changes to a p-type with a 9e+12/cm-3 concentration.
- The surface charge density increases to 5e+14 /cm-2 .

- Chaouki, Boulahouache

- January 22, 2001

**Notes:**
Check for the right parameters.

## n+ and p+ Doping profiles for P-stop structure.

- The n+ doping profile is,
-  Gaussian distribution:
- PeakValue = 1e+20 / cm-3
- ValueAtDepth = 2e+12 /cm-3
- Depth = 4.5 m
- The p+ doping profile is,
-   Gaussian function distribution:
- PeakValue = 6e+18 / cm-3
- ValueAtDepth = 1e+11 /cm-3
- Depth = 1.75 m

- Chaouki, Boulahouache

- January 22, 2001

## p+ Doping profile for P-spray structure.

- The p+ doping profile is,
-   Error function distribution:
- maxValue = 6e+18 / cm-3
- ValueAtDepth = 1e+11 /cm-3
- Depth = 1 m

- Chaouki, Boulahouache

- January 22, 2001

## n+ density distribution for P-stop and P-spray structures before irradiation.

- Chaouki, Boulahouache

- January 22, 2001

## Interpixel P+ Distribution.

- For p-stop structure

- For p-spray structure

- Chaouki, Boulahouache

- January 22, 2001

## Electrostatic field distribution.

- For p-stop structure

- For p-spray structure

- Chaouki, Boulahouache

- January 22, 2001

## Vector Presentation Of The Electric Field

- For p-stop structure

- For p-spray structure

- Chaouki, Boulahouache

- January 22, 2001

## Lateral field distribution and p-density along the X-axis.

- For p-stop structure

- For p-spray structure

- Lateral Electric Field

- Lateral Electric Field

- p+ distribution

- p+ distribution

- pink  p+ distribution
- green  lateral electric field

- Chaouki, Boulahouache

- January 22, 2001

## Lateral field distribution and n-density along the X-axis.

- For p-stop structure

- For p-spray structure

- Lateral Electric Field

- Lateral Electric Field

- n+ distribution

- n+ distribution

- red  lateral electric field
- green  n+ distribution

- Chaouki, Boulahouache

- January 22, 2001

## Characteristics of the lateral field (Before irradiation)

- Before irradiation the maximum lateral field,
- For p-stop structure is 2.277e+05 V/cm which is a factor of 1.9 higher than the number given in a paper done by Rohe et al. paper*.
- For p-spray structure is 1.719e+06 V/cm which is a factor of 4.5 higher than the number given in the same paper.

- *Rohe et al. / Nucl. Instr. And Meth. In  Phys. Res. A 409 (1998) 224-228.

- Chaouki, Boulahouache

- January 22, 2001

## Interpixel P+ Distribution.

- For p-stop structure

- For p-spray structure

- Chaouki, Boulahouache

- January 22, 2001

## Lateral field distribution and p-density along the X-axis.

- For p-spray structure

- For p-stop structure

- pink  p+ distribution
- green  lateral electric field

- red  lateral electric field
- green  p+ distribution

- Lateral Electric Field

- Lateral Electric Field

- p+ distribution

- p+ distribution

- Chaouki, Boulahouache

- January 22, 2001

## Lateral field distribution and n-density along the X-axis.

- For p-spray structure

- For p-stop structure

- red  lateral electric field
- green  n+ distribution

- n+ distribution

- n+ distribution

- Lateral Electric Field

- Lateral Electric Field

- Chaouki, Boulahouache

- January 22, 2001

## After irradiation the maximum lateral field,
For p-stop structure is 1.263e+06 V/cm which is a factor of 2.6 higher than the number given in Rohe paper.
For p-spray structure is 1.200e+06 V/cm which is a factor of 6 higher.

- For p-stop structure is 1.263e+06 V/cm which is a factor of 2.6 higher than the number given in Rohe paper.
- For p-spray structure is 1.200e+06 V/cm which is a factor of 6 higher.

- Characteristics of the lateral field (after irradiation)

- Chaouki, Boulahouache

- January 22, 2001

## Oxide Charge Effect...

- By increasing the surface charge density one can assess the effect of a hard radiation damage on both kinds of pixels. The following table will include simulations done for different surface charge densities,

- Surface Charge Density

- Chaouki, Boulahouache

- January 22, 2001

## Lateral field-oxide charge correlation

| Surface Charge density | P-stop pixels | P-spray pixels |
| --- | --- | --- |
| 3*1010/cm-2 | 1.675*105 V/cm | 1.873*106 V/cm |
| 3*1011/cm-2 | 2.310*105 V/cm | 1.870*106 V/cm |
| 3*1012/cm-2 | 8.426*105 V/cm | 1.830*106 V/cm |

- Chaouki, Boulahouache

- January 22, 2001

## Simplified model of structuredescribed in "graded p-spray from SINTEF, Hera-B detectors"

- The n+ doping profile is,
-  Gaussian distribution:
- PeakValue = 1e+18 /cm-3
- diffLength = 1.63 m
- The p+ doping profile has two pieces,
- 1) Error function distribution:
- maxValue = 6e+16 /cm-3
- diffLength = 0.47 m.
- 2) Gaussian distribution:
- PeakValue = 6e+16 /cm-3
- PeakPosition = 1 m
- diffLength = 0.47 m.
- The Bias voltage is at –200 volts

- Chaouki, Boulahouache

- January 22, 2001

## P+ and E-field Distributions for r=1*10+10 cm-2...

- Chaouki, Boulahouache

- January 22, 2001

## P+ and E-field Distributions for r=2*10+11 cm-2 ...

- Chaouki, Boulahouache

- January 22, 2001

## P+ and E-field Distributions for r=1*10+12 cm-2 ...

- Chaouki, Boulahouache

- January 22, 2001

## Total Electric Field distribution.

- The total electric filed distribution at a distance of 0.47m away from the surface.
- The maximum electric field (for =1*1010cm-2) is about 4.4*105V/cm, it is a factor of 3 higher than the maximum field of the real graded p-spray structure(1.6*105V/cm).

- Black  for =1*1010cm-2
- red  for =2*1011cm-2
- Blue  for =1*1012cm-2

- Lateral Distance (m)

- Total Electric Field

- Chaouki, Boulahouache

- January 22, 2001

## Conclusion...

- The oxide charge is a key element that affects the lateral field in n+/n/p+ pixel structures.
- P-spray detectors need to have enough p+ doping to compensate the inversion layer up to the saturation charge in the oxide, thus they start with very high lateral fields. P-stop starts with lower lateral fields, but their properties deteriorate with the increased radiation level.

- Chaouki, Boulahouache

- January 22, 2001