1. Andrew Clarke First Year PhD Student Modelling Charge Storage In Euclid Device Structures

2. Introduction Euclid Mission Weak Lensing Radiation damage
Device modelling
Charge packet modelling
Future work

3. Euclid Mission
Euclid is a proposed ESA mission to map the geometry of the dark Universe.
Its main aim is to complete a weak lensing survey using a wide field imager.
The CCD used will be the CCD273.
Mission lifetime: 5years.

4. Radiation Damage
Displacement caused by the radiation damage can cause vacancies which are mobile.
The vacancies can become thermodynamically stable when they meet a phosphorus atom, usually in the buried channel and create an electron trap.
Traps will occur most often in the buried channel and CTE will be effected.

5. Radiation Damage Models

6. Interaction Volume
The volume occupied by charge packets is directly related to the CTI characteristics of the device. It is important to model the charge storage in the Euclid device structures to produce realistic charge transfer and radiation damage models for the Euclid mission.
When 0<β<1 both charge density and volume change as charge is added to the packet.

7. Euclid Models Euclid Pixel Electrodes Euclid Register Substrate
Serial readout register
12µm x 12µm
The pixel is the same in both the CCD273 and CCD204 devices.
The picture shows the pixel model, with the internal potential field present when voltage is applied to the electrodes.
The red area is high potential and is the area where the charge packets will be confined.
The pixel is 4 phase with an alternating electrode structure: 2µm and 4µm, and is operated so that two adjacent electrodes are always active.
This maximises FWC as the potential well will occupy approximately half the structure.
12µm x 50µm (CCD273) Or
12µm x 80µm (CCD204)

8. Measuring the charge packet

9. Volume Models: Pixel
The volume follows a curve similar to that expected from the interaction volume function.

10. Volume Models: Register
Straight lines can be fitted to the log plots to give simple functions, these approximate the ‘trapping volumes’ occupied by the charge packet in each device structure.
Functions in the form:

11. Comparing Structures

12. Comparing Structures

13. Relative Volume
Comparing the volume occupied by charge packets in the registers of the CCD204 and the CCD273.

14. Conclusions
Models agree with expected values for the devices, the Signal-volume trend appears to agree with theory.
Functions can be extracted from the Signal-volume plots to be improve the radiation damage models of Euclid devices.
The decrease in charge storage volume from the CCD204 to the CCD273 meets expectation for small signal (Ne<1000), where it matters.
Further work will involve verification of the model parameters.