Field effect transistor test structures for inter-strip isolation studies in silicon strip detectors

Abstract

Its radiation resilience has established p-type silicon as tracking detector baseline material in upcoming high-luminosity physics experiments. Electric isolation of n+ electrodes with p+ implants (p-stop or p-spray) is crucial for segmented p-type sensor quality. P+ doping concentration, implantation depth, and geometry determine the achievable resistance between segments. Typically, inter-strip resistance is measured directly on the strip sensors. Large resistances on the order of 100GΩ require precise, low-noise current measurements, which are strongly influenced by parasitic currents. To provide a comparably simple alternative to measurements on strip sensors, this contribution seeks to relate Metal-Oxide–Semiconductor Field-Effect Transistor (MOSFET) threshold voltage to sensor inter-strip resistance. We utilize circular MOSFET test structures fabricated on the same wafers as the strip sensors. This paper compares measurements of MOSFETs and strip sensors on wafers with different n- and p-spray implantations and presents comparative TCAD simulations. MOSFET test structures could present a fast option to judge silicon sensor inter-strip resistance and strip isolation properties. Process quality control during future series productions can benefit from this technique.