Characterization of silicon micro-strip sensors with a pulsed infra-red laser system for the CBM experiment at FAIR

Abstract

The Compressed Baryonic Matter (CBM) experiment at FAIR is composed of 8 tracking stations consisting of 1292 double sided silicon micro-strip sensors. For the quality assurance of produced prototype sensors a laser test system (LTS) has been developed. The aim of the LTS is to scan sensors with a pulsed infra-red laser driven by step motor to determine the charge sharing in-between strips and to measure qualitative uniformity of the sensor response over the whole active area. The prototype sensors which are tested with the LTS so far have 256 strips with a pitch of 50 μm on each side. They are read-out using a self-triggering prototype read-out electronic ASIC called n-XYTER. The LTS is designed to measure sensor response in an automatized procedure at several thousand positions across the sensor with focused infra-red laser light (spot size ≈ 12 μm , wavelength = 1060 nm). The pulse with duration (≈ 10 ns) and power (≈ 5 mW) of the laser pulses is selected such, that the absorption of the laser light in the 300 μm thick silicon sensors produces a number of about 24000 electrons, which is similar to the charge created by minimum ionizing particles (MIP) in these sensors. Laser scans different prototype sensors is reported.

Non-invasive characterization and quality assurance of silicon micro-strip detectors using pulsed infrared laser

“…A systematic procedure for the characterization [9,10] and quality assurance [4] has been developed for the prototype sensors. Laser test stand (LTS) has been the next step to investigate uniformity, integrity of the sensors.…”

“…The laser characterization set-up (LTS) is composed of 7 constituent blocks namely, (a) infra-red laser, (b) detector module, (c) front-end electronics, (d) step motor, (e) power supplies, (f) data acquisition and (g) device controls. The laser test system configuration and its components is briefly described in previous publication [10].…”

“…The LTS has developed certain characterization procedures to determine the charge sharing in-between strips and to measure qualitative uniformity of the sensor response over the whole active area (discussed in succeeding sections). The prototype sensors which are tested with the set-up are small prototype sensors (256 strips, pitch = 50 µm on each side) (reported last year [10]) and full size detector modules (1024 strips/side and pitch = 58 µm). They are read-out using a self-triggering prototype read-out electronic ASIC called n-XYTER.…”

“…• Non-invasive methods are the characterization and investigation of performance based on methods which do not require physical contact of mechanical probes to the sensor or detector module. The important features are: (i) a few significant parameters of the DUT can be investigated, (ii) leaves no scratches or marks on the surface, (iii) not limited to sensors and also viable to test detector modules and (iv) method involves injection of localized charge using a pulsed infra-red laser for QA [5].…”