/sintefimage.png)
The aim of this project is to complete the development of a laser scanning setup to be used for Transient Current Technique (TCT) characterisation of silicon radiation detectors. This technique can provide excellent feedback on the operation of silicon detectors in terms of signal efficiency and response uniformity. It is often used to characterise the response of novel silicon sensor designs. The measurement uses sub-nanosecond laser pulses to generate free charge carriers into a silicon sensor. The motion of the free charge carriers induces an electrical signal at the sensor electrodes that can be collected and processed in different ways: (i) using wideband current transimpedance amplifiers to study the timing evolution of the signal for different hit positions and sensor operating voltages and (ii) using charge amplifiers to estimate the amount of total collected charge for different hit positions. The laser is scanned over the area of interest in 2-dimensional in order to achieve heat maps of the sensor response, aiming at the identification of possible flaws or further improvement in a sensor design.
Fig. 1 shows the basic components to be used in this project. The first version of the laser scanning system will be composed of laser diodes coupled to an optical fibre delivering the light pulses to a focusing lens that will focus the light onto the sensor under test. The sensor will be mounted on a high precision positioning stage (3-axes) that automatically scans the sensor across the laser beam. The main components of the system are:
1) Laser driver: in-house built laser driver producing sub-nanosecond pulses with repetition of 100Hz
2) Laser diode: commercial laser diodes with power in the range from 1 to 50 mW and wavelengths over the full visible spectrum, near infra-red and infrared.
3) Laser coupling system: used to install the laser diode, collimate the light produced and feed the light into the optical fibre (Thorlabs).
4) Focuser: to focus the light transported by the optical fibre to a spot size of about 5µm.
5) Sensor: different type of silicon sensors produced by SINTEF.
6) Sensor positioning system: a 3-axes position system (Thorlabs) will be used to change the focusing depth and to perform a raster scan of the sensor across the laser beam. The movement of the stage will be performed with high precision motorized actuators controlled by Python.
7) Power meter: to monitor the beam transmitted power (Thorlabs)
8) Readout electronics: basic readout electronics for silicon detectors.
9) Standard lab instruments: power supply, oscilloscopes etc…
The measurements results can be cross-checked and validated using finite-element numerical simulations using SYNOPSYS SENTAURUS advanced TCAD tools, available at SINTEF.
TASKS to be performed:
1) Characterise the operation of the laser driver using laser diodes and propose possible improvements to its design. This task might include PCB design.
2) Develop, refine and document the laser diode coupling procedure to the optical fibre.
3) Write and test the Python code used for positioning of the sensor and for the automatic raster scanning. A basic version of the necessary code is already available but needs to be optimised.
4) Write and test the Python code to acquire the data from the readout electronics and from the oscilloscope.
5) Test the full system using SINTEF silicon detectors.
6) Develop a numerical model for the sensor under test and its interaction with laser pulses using the SYNOPSYS SENTAURUS TCAD tools.
Additional OPTIONAL tasks:
1) Learn the techniques used for electrical validation and characterisation of silicon radiation detectors on wafer, using the manual probe-station in the clean-room.
2) Design carrier PCBs for sensor assembly.
3) Learn to perform the assembly of silicon radiation detectors onto PCBs and perform the wire bonding using the wire-bonding machine available at SINTEF.
Required qualifications:
1) Basic understanding of semiconductor physics and P-N junction operation
2) Understanding of basic electronics circuits and their behaviour
3) Understanding of basic notions on Printed Circuit Board design and production
4) Basic knowledge of optics and light transport in optical fibres can be useful
5) Good knowledge of the Python programming language:
• Some of the modules that can be useful are: pyVISA, Matplotlib, scipy, numpy
The project is suitable for a specialization project and master project. It is required that the Master project is carried out on-site at SINTEF MiNaLab in Oslo. The specialization project could be remote, but doing some work periods at MiNaLab will be advantageous. NTNU supervisor is Jostein Grepstad, supervisor at MiNaLab will be Marco Povoli.