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

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

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.

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.

Radiation Damage Models

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.

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)

Measuring the charge packet

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

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:

Comparing Structures

Comparing Structures

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

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.