Speaker
Description
The ITk Strip is a silicon-strip charged-particle detector that is going to be installed in the ATLAS experiment for the HL-LHC. GaNFETs are radiation-tolerant transistors that permit switching off high voltage to malfunctioning sensors. To ensure the reliability of the GaNFETs in the high radiation environment expected for the ITk Strip, a sample of the transistors were exposed to gamma and heavy ion radiation. The GaNFETs were characterized pre- and post- irradiation, and their state was monitored during irradiation. We will report on the results of these irradiations.
Summary (500 words)
The LHC will be upgraded to the HL-LHC which will significantly increase the instantaneous luminosity. The result is a busier charged-particle tracking system along with a harsher radi- ation environment for all the detector components. To guarantee the success of the ATLAS experiment, the ATLAS inner detector will be upgraded with the Inner Tracker (ITk), an all- silicon based tracking system consisting of two subsystems: ITk Pixel and ITk Strip. The ITk Strip is composed of a barrel with silicon-strip staves and two end-caps made of silicon-strip petals which surround the ITk Pixel detector. The ITk Strip staves consist of 14 modules on each side of a carbon composite structure. Each module houses two types of ASICs responsible for data readout: ATLAS Binary Chip (ABCStar) and Hybrid Control Chip (HCCStar). In addition, each module contains an Autonomous Monitoring and Control Chip (AMACStar) and a GaNFET.
Each ITk Strip stave side is split into 4 segments. Each segment has a single high voltage line that is distributed to each of its corresponding modules in a daisy chain form. If one module in a stave segment fails and the high voltage (HV) line is interrupted, the full segment becomes dysfunctional. To avoid losing multiple modules from a single HV line failure, GaNFETs, custom designed radiation-tolerant transistors, were installed in each module’s power board to be operated as HV switches. The GaNFETs drain-source voltage is the module’s HV and the GaNFET state is controlled by the AMACStar by providing either 0V or 3.3V to the gate.
The radiation tolerance design of these FETs needs to be tested to ensure their operability throughout the HL-LHC lifetime. The GaNFETs were exposed to mainly 2 types of radia- tion at Brookhaven National Laboratory: gamma and heavy ions. The gamma irradiation is used to study the effects of total ionizing dose on the transistors like current leakages. The heavy ion irradiation is used to study the more common transistor failure modes: single event burnout (SEB) and single event gate rupture (SEGR). SEB and SEGR are caused due to large energy depositions by a single particle on a localized region of the transistor that causes it to break or to produce a conducting path through the GaNFETs gate oxide. SEB and SEGR are effects that are rarely produced by protons or neutrons. In order to gather significant statistics of these effects, the GaNFETs are irradiated with heavy ions with significantly higher linear energy transfers than the expected ones from hadrons at the HL-LHC.
In this presentation, we will report our GaNFET studies findings.
