LCFI Mechanical room• LCFI facilities

– Cold survey cryostat and LASS, currently being upgraded

– Cold gas test rig– Glue robot

• All housed in Lab 9– Temperature controlled– Gas supplied externally– Gowning area, plan on

keeping as a clean area once LASS upgrade complete

• LASS upgrade– Higher resolution– Smaller non linearity effects– Result: higher precision

measurements

Optical bencharea

LCFI gas services

Laminar flow bench Glue robotWork desk

Student test rig

Cold survey cryostat and LASS

Silicon Stress studies

• Want an idea of force required to hold silicon sensor down flat

• Determine effect of each material used in the silicon sensor and make a ranking system to working out which has the largest effect.

• From Glenn Christians thesis VXD3 silicon sensors 15mm x 100mm and thinned to 13um curl across the width where the distance between the base and the peak of the curl (h) was 0.8mm

• Silicon sensors for FLC will be 25mm x 250mm

0.8mm

Silicon Stress Studies

• Assumptions:– FLC silicon sensors have a curl that would be the same radius of

curvature if thinned to 13um– 1um layer of aluminium on surface of silicon sensors– All curl is across width– Curl caused by CTE mismatch between silicon and Aluminium

• First determined h for silicon sensor 25mm x 250mm to be 2mm

• By FEA found temperature change to create this curl to be a change of 44 degrees

• Thickened device to be 25um thick and found:– Curl – 531um

Silicon Stress Studies

• Applied a distributed load to flatten the silicon and found:

Total load < 0.055 Newton's

Total load ~ 0.055 Newton's

Total load > 0.055 Newton's

Silicon Stress Studies

• Ranked material by resulting curl for a temperature change of 44 degrees

Material Thickness (um) Curl (um)

Aluminium 1 531

Polyamide 1 78

Silicon Dioxide 1 -49

Silicon Nitride 0.085 3

Polysilicon 0.3 -2

Silicon Stress Studies

• From these results will be able to estimate the stiffness of the substrate required to hold the silicon sensors flat

• But…– Results suggest aluminium is driving the curling– Would suggest processed wafers curl towards processed side– In Reality wafers curl away from processed side

• Aluminium not driving the curl, needs further study

Would expect Observed

Plans

• Complete upgrade to LASS– Complete Labview software– Ensure any mechanical parts needed are

fitted– Test fully

• Build engineering model with glue robot• Build Silicon/RVC ladder with glue robot• Test existing Silicon/SiC ladder on LASS• Test Silicon RVC on LASS