DEPFET sensors, A Test Case To Study 3d Effects

Abstract

DEPleted Field Effect Transistors are inherently 3d structures, collecting carriers due to X-rays in a potential well beneath a gate controlled MOSFET channel. This charge modulates the MOSFET current and has to be removed periodically into a direction orthogonal to the MOSFET channel. The amplitude of the modulation is 10−2 of the drain current and has to be computed with errors smaller 10−3. To reach this goal, test functions are introduced, which solve the related adjoint discrete problem and cancel the first order error terms for each terminal current. The proper ‘discrete integration by parts’ reduces rounding and allows to compute the current balance for typical conditions with a relative error smaller than 10−12.