Characteristics of 2N4416 Si JFETs for radiation spectrometer charge sensitive preamplifiers

The input transistors (JFETs) of feedback resistor-less charge sensitive preamplifiers (CSPs), for photon and charged particle counting radiation spectrometers, that use semiconductors as their detectors, are operated in an unusual forward biased mode; consequently, manufacturer datasheets cannot necessarily be relied upon, as they do not specify the characteristics of the JFETs when they are operated with the gate-to-source junction forward biased. This experimental study, in which 165 2N4416 and 2N4416A NJ26 silicon junction field effect transistors (JFETs) were electrically characterised at ambient laboratory temperature, focused on the JFETs’ performances in the context of their use as input transistors of feedback resistor-less charge sensitive preamplifiers (CSPs). The experimental study found evidence which supports much of the common practice of the skilled CSP designer but which had not been documented with results in the open literature until now. This includes, inter alia, that: the 2N4416 performs better than the 2N4416A; not all transistors even of the same type have comparable performance when operated in forward bias mode; only a small proportion of 2N4416 and 2N4416A transistors are of desirable performance characteristics for CSPs; and, individual screening of each candidate JFET is required if an optimally performing CSP is to be produced – even when using JFETs of the same type from the same batch. The methodology and analysis documented here will also be useful to researchers developing new wide bandgap semiconductor JFETs for high temperature tolerant and radiation-hard CSPs.