Advanced LGADs with improved radiation hardness and ultra-transparent entrance windows
Lead Research Organisation:
University of Glasgow
Department Name: School of Physics and Astronomy
Abstract
Hybrid silicon detectors have revolutionized the detection and measurement of radiation.
The range of applications are vast and include: detectors for fundamental physics (e.g., particle, nuclear, astronomy and solar physics), in our understanding of biology and materials at synchrotron facilities and in electron microscopes, and even radiation monitoring of astronauts on the international space station.
The best hybrid pixels detectors count individual photos incident on the sensor. These devices are noiseless due to the use of a discriminator after the first amplification stage. This discriminator results in a lowest possible detectable energy of the incident radiation. The most performant photon counting hybrid detectors have a minimum threshold that corresponds to a minimum detectable X-ray energy of 2keV. The noise contributions at the input of the front-end amplifier are due to detector capacitance, leakage current and inductance. The spatial resolution of the most advanced hybrid pixel detectors (e.g. TimePix and Dectris detectors) are order 16um obtained with 50um pixels. The temporal resolution of the most advance TimePix4 is 200ps, while the next generation proposed for the VELO-II upgrade (PicoPix) will have 20ps timing resolution. To take advantage of the increased electronics time resolution, the sensors need to be improved from standard planar devices. Such detectors are thin low gain avalanche detectors (LGAD) or 3D detectors. To allow lower energy detection the sensor must have a near transparent backside contact to allow transmission of the incoming low energy radiation. The sensor must also have reduced input noise on the front-end amplifier and therefore low capacitance and ideally have internal gain. The LGAD device has a lower capacitance than a 3D detector and due to the internal gain can further reduce the minimum detectable incident radiation as well as produce excellent 20ps timing resolution. The trench LGAD is able to produce uniform gain over a 50um pitch pixel array, unlike a 3D detector with its intrinsic dead space. These characteristics place the LGAD at an advantage over the 3D detector for low energy detection.
This project will develop a small pixel thin LGAD device to obtain 20ps timing resolution with an ultra-transparent backside contact for extremely low energy detection bonded to a TimePix4 pixel chip. The goal is to have 20ps timing resolution with a minimum detectable X-ray energy of 250 eV. These are an order of magnitude improvements on the state-of-the-art.
The immediate applications of these devices are soft and tender X-ray detection at synchrotrons which are key for imaging of low atomic number elements that are responsible for many biological functions as well as being key to understanding future energy storage materials.
In addition to low energy X-ray detection many applications demand radiation hardness. The project will also develop the most radiation hard LGAD devices by making a systematic investigation, first be simulation and then fabrication, into the effects of doping profiles and background dopant types on radiation hardness. Radiation hardness will be tested for both protons and X-rays.
The most immediate application of a radiation enhanced LGAD will be in particle and nuclear physics.
The range of applications are vast and include: detectors for fundamental physics (e.g., particle, nuclear, astronomy and solar physics), in our understanding of biology and materials at synchrotron facilities and in electron microscopes, and even radiation monitoring of astronauts on the international space station.
The best hybrid pixels detectors count individual photos incident on the sensor. These devices are noiseless due to the use of a discriminator after the first amplification stage. This discriminator results in a lowest possible detectable energy of the incident radiation. The most performant photon counting hybrid detectors have a minimum threshold that corresponds to a minimum detectable X-ray energy of 2keV. The noise contributions at the input of the front-end amplifier are due to detector capacitance, leakage current and inductance. The spatial resolution of the most advanced hybrid pixel detectors (e.g. TimePix and Dectris detectors) are order 16um obtained with 50um pixels. The temporal resolution of the most advance TimePix4 is 200ps, while the next generation proposed for the VELO-II upgrade (PicoPix) will have 20ps timing resolution. To take advantage of the increased electronics time resolution, the sensors need to be improved from standard planar devices. Such detectors are thin low gain avalanche detectors (LGAD) or 3D detectors. To allow lower energy detection the sensor must have a near transparent backside contact to allow transmission of the incoming low energy radiation. The sensor must also have reduced input noise on the front-end amplifier and therefore low capacitance and ideally have internal gain. The LGAD device has a lower capacitance than a 3D detector and due to the internal gain can further reduce the minimum detectable incident radiation as well as produce excellent 20ps timing resolution. The trench LGAD is able to produce uniform gain over a 50um pitch pixel array, unlike a 3D detector with its intrinsic dead space. These characteristics place the LGAD at an advantage over the 3D detector for low energy detection.
This project will develop a small pixel thin LGAD device to obtain 20ps timing resolution with an ultra-transparent backside contact for extremely low energy detection bonded to a TimePix4 pixel chip. The goal is to have 20ps timing resolution with a minimum detectable X-ray energy of 250 eV. These are an order of magnitude improvements on the state-of-the-art.
The immediate applications of these devices are soft and tender X-ray detection at synchrotrons which are key for imaging of low atomic number elements that are responsible for many biological functions as well as being key to understanding future energy storage materials.
In addition to low energy X-ray detection many applications demand radiation hardness. The project will also develop the most radiation hard LGAD devices by making a systematic investigation, first be simulation and then fabrication, into the effects of doping profiles and background dopant types on radiation hardness. Radiation hardness will be tested for both protons and X-rays.
The most immediate application of a radiation enhanced LGAD will be in particle and nuclear physics.
People |
ORCID iD |
| Richard Bates (Training Grant Holder) |