16-08-2012, 10:11 AM
Geiger-Mode Avalanche Photodiodes in Particle Detection
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Introduction
The International Linear Collider (ILC) [1] and the Compact Linear Collider (CLIC) [2] are two proposed e+e- high precision colliders which currently are in their technical design phase. The scope of theses colliders is to provide measurements with unprecedented accuracy and precision. Appropriate detector systems capable of precisely measuring the direction of particle tracks are needed in order to fully exploit the research potential of any particle accelerator. Nevertheless, the future e+e- linear colliders put challenging requirements on detector systems since they will have to supply exceptional position resolution at high incoming rates. At present time, there is no mature technology that can fulfill these specifications and new detector systems are being developed in parallel with the accelerator. Solid-state sensor technologies concentrating most of the research, which are based on CMOS monolithic pixel sensors, are Charge Coupled Devices (CCDs) [3], Monolithic Active Pixel Sensors (MAPS) [4], DEPleted Field Effect Transistors (DEPFETs) [5] and Geiger mode Avalanche PhotoDiodes (GAPDs) [6, 7]. Alternative approaches are based on Silicon-On-Insulator (SOI) devices [8]. However, none of the presented candidates meets all the requirements imposed by the collider. Several research groups are currently working towards their improvement. More recently, CMOS sensors exploiting vertical integration technology have also gained interest [9]. This alternative may have the highest potential, but it will need more time to reach maturity.
Test beam set-up
The set-up for the test beam consists of two GAPD bidimensional arrays (which are the Design Under Test or DUT), two Printed Circuit Boards (PCBs), two FPGAs, an EUDET/AIDA telescope and two scintillator fibres. Additionally, a Trigger Logic Unit (TLU) is used to distribute the trigger signal. A schematic diagram of the test beam set-up is depicted in figure 1.
GAPD detector prototype
The GAPD detector was prototyped with the standard HV-AMS (High-Voltage AustriaMicrosystems) 0.35μm CMOS technology (h35b4). The detector was designed to have a sensitive area of 1mmx1mm in order to facilitate the observation of particle traces. In addition, the sensor size was fixed to 22.9μmx100μm [11] to achieve a good fill factor (88%). The detector is organized in 10 rows (m) per 43 columns (n) of pixels. Each pixel of the detector combines a sensor and proper readout electronics (see figure 2 for pixel schematics). Both the sensor and the readout electronics have been monolithically integrated on a single CMOS die. Given that the scope of the GAPD array is to prove the efficiency of the detector in a test beam, radiation tolerance has not been considered.
Satellite electronics
In order to reduce the distortion in the particle path caused by the test set-up materials, the silicon wafer of the chip will be thinned down to 250μm. In addition, the naked die without package will be wire bonded directly to the PCB, which will be perforated under the chip. An ALTERA Cyclone IV FPGA-based control board by terasIC will be used to generate the fast logic control signals (RST, INH, CLK1 and CLK2m) and also to count off-chip the number of pulses generated by the sensor. Two layers of GAPDs will be used to discard the false counts due to the noise.
To characterize the performance of the DUT during the test beam, it is necessary to determine the tracks of the used test beam particles very precisely with a reference system. The resolution of the device used for this purpose should be higher than the expected intrinsic resolution of the DUT.
Expected results
At current time, two GAPD test beams are already planned. The first test beam, which will be a preparation for the final one, will take place at DESY with a 6GeV electron beam. The final test beam will be carried out at CERN with a 120GeV pion beam. In order to know in advance the expected test beam measurement results, simulations have been run with Geant4. To obtain reliable simulation results, the study has been performed including all the different materials that are going to be used in the test beam. Different distances of 2cm and 10cm between the DUT and the last telescope layer have also been considered.
The results of the simulations indicate that there exists a certain amount of distortion associated to the position for which the particle has passed. Since the distortion increases with the distance, it is necessary to place the DUT and the EUDET/AIDA telescope as close as possible. In addition, the expected distortion at DESY is higher than at CERN. In particular, for a DUT-telescope distance of 2cm, the distortion will be about 16μm at DESY and about 0.5μm at CERN. According to these results, and given that the pixel width is 22.9μm, it will be possible to distinguish detection between neighbour pixels at DESY and within a pixel at CERN. Moreover, we also expect to characterize the efficiency of the sensor as a function of the position and the time, the crosstalk, the spatial resolution and the two-track resolution. The measurements will be repeated for different overvoltages.
Conclusion
A GAPD array has been designed and fabricated with a standard CMOS technology to prove the efficiency of the sensor in a test beam. The detector has 1mmx1mm of sensitive area to fit the test beam requirements. In addition, it can be operated in the gated mode to synchronize
LCWS11
the sensor active periods with the expected signal arrival as well as to reduce the detected noise. The set-up will consist of two GAPD arrays, two PCBs, two FPGAs, an EUDET/AIDA telescope, two scintillator fibres and a TLU. At present time, two test beams, at DESY and at CERN, are already planned, where we expect to characterize the GAPD response to high energetic particles. The results of the test beam will confirm or refute the validity of the proposed sensor as a candidate for tracker detector at the future linear collider.
[attachment=31587]
Introduction
The International Linear Collider (ILC) [1] and the Compact Linear Collider (CLIC) [2] are two proposed e+e- high precision colliders which currently are in their technical design phase. The scope of theses colliders is to provide measurements with unprecedented accuracy and precision. Appropriate detector systems capable of precisely measuring the direction of particle tracks are needed in order to fully exploit the research potential of any particle accelerator. Nevertheless, the future e+e- linear colliders put challenging requirements on detector systems since they will have to supply exceptional position resolution at high incoming rates. At present time, there is no mature technology that can fulfill these specifications and new detector systems are being developed in parallel with the accelerator. Solid-state sensor technologies concentrating most of the research, which are based on CMOS monolithic pixel sensors, are Charge Coupled Devices (CCDs) [3], Monolithic Active Pixel Sensors (MAPS) [4], DEPleted Field Effect Transistors (DEPFETs) [5] and Geiger mode Avalanche PhotoDiodes (GAPDs) [6, 7]. Alternative approaches are based on Silicon-On-Insulator (SOI) devices [8]. However, none of the presented candidates meets all the requirements imposed by the collider. Several research groups are currently working towards their improvement. More recently, CMOS sensors exploiting vertical integration technology have also gained interest [9]. This alternative may have the highest potential, but it will need more time to reach maturity.
Test beam set-up
The set-up for the test beam consists of two GAPD bidimensional arrays (which are the Design Under Test or DUT), two Printed Circuit Boards (PCBs), two FPGAs, an EUDET/AIDA telescope and two scintillator fibres. Additionally, a Trigger Logic Unit (TLU) is used to distribute the trigger signal. A schematic diagram of the test beam set-up is depicted in figure 1.
GAPD detector prototype
The GAPD detector was prototyped with the standard HV-AMS (High-Voltage AustriaMicrosystems) 0.35μm CMOS technology (h35b4). The detector was designed to have a sensitive area of 1mmx1mm in order to facilitate the observation of particle traces. In addition, the sensor size was fixed to 22.9μmx100μm [11] to achieve a good fill factor (88%). The detector is organized in 10 rows (m) per 43 columns (n) of pixels. Each pixel of the detector combines a sensor and proper readout electronics (see figure 2 for pixel schematics). Both the sensor and the readout electronics have been monolithically integrated on a single CMOS die. Given that the scope of the GAPD array is to prove the efficiency of the detector in a test beam, radiation tolerance has not been considered.
Satellite electronics
In order to reduce the distortion in the particle path caused by the test set-up materials, the silicon wafer of the chip will be thinned down to 250μm. In addition, the naked die without package will be wire bonded directly to the PCB, which will be perforated under the chip. An ALTERA Cyclone IV FPGA-based control board by terasIC will be used to generate the fast logic control signals (RST, INH, CLK1 and CLK2m) and also to count off-chip the number of pulses generated by the sensor. Two layers of GAPDs will be used to discard the false counts due to the noise.
To characterize the performance of the DUT during the test beam, it is necessary to determine the tracks of the used test beam particles very precisely with a reference system. The resolution of the device used for this purpose should be higher than the expected intrinsic resolution of the DUT.
Expected results
At current time, two GAPD test beams are already planned. The first test beam, which will be a preparation for the final one, will take place at DESY with a 6GeV electron beam. The final test beam will be carried out at CERN with a 120GeV pion beam. In order to know in advance the expected test beam measurement results, simulations have been run with Geant4. To obtain reliable simulation results, the study has been performed including all the different materials that are going to be used in the test beam. Different distances of 2cm and 10cm between the DUT and the last telescope layer have also been considered.
The results of the simulations indicate that there exists a certain amount of distortion associated to the position for which the particle has passed. Since the distortion increases with the distance, it is necessary to place the DUT and the EUDET/AIDA telescope as close as possible. In addition, the expected distortion at DESY is higher than at CERN. In particular, for a DUT-telescope distance of 2cm, the distortion will be about 16μm at DESY and about 0.5μm at CERN. According to these results, and given that the pixel width is 22.9μm, it will be possible to distinguish detection between neighbour pixels at DESY and within a pixel at CERN. Moreover, we also expect to characterize the efficiency of the sensor as a function of the position and the time, the crosstalk, the spatial resolution and the two-track resolution. The measurements will be repeated for different overvoltages.
Conclusion
A GAPD array has been designed and fabricated with a standard CMOS technology to prove the efficiency of the sensor in a test beam. The detector has 1mmx1mm of sensitive area to fit the test beam requirements. In addition, it can be operated in the gated mode to synchronize
LCWS11
the sensor active periods with the expected signal arrival as well as to reduce the detected noise. The set-up will consist of two GAPD arrays, two PCBs, two FPGAs, an EUDET/AIDA telescope, two scintillator fibres and a TLU. At present time, two test beams, at DESY and at CERN, are already planned, where we expect to characterize the GAPD response to high energetic particles. The results of the test beam will confirm or refute the validity of the proposed sensor as a candidate for tracker detector at the future linear collider.