Manufacturing Process for Ceramic Encapsulated Junction Field Effect Transistors (JFETs) and Statistical Evaluation of JFET Header Dielectric Materials

Abstract

Electronic noise is the ultimate resolution limiting factor in non-dispersive low energy X-ray spectrometers. Lossy dielectric materials in the input of the spectrometer's charge-sensitive preamplifier contribute significant amounts of noise. In particular, the glass insulating header of the input JFET produces a major portion of this dielectric noise. A previous small experimental lot of JFETs encapsulated with low loss ceramic headers exhibited significantly lower electronic noise than JFETs with lossy glass headers containing the same type JFET chip. A larger lot of JFETs (~350) encapsulated with 99% BeO ceramic headers has been prepared under standard transistor production conditions. Processing details are reported as well as statistical analyses of noise and other electrical measurements obtained on a random sample from this production lot. Similar data are reported for commercial JFETs containing the same type chip (TI-2N4416) encapsulated in an epoxy body and encapsulated with glass headers. In addition, measurements have been obtained for JFET chips mounted on high purity Al2O3 (99.5%) thin flat substrates. These substrates, normally used for integrated circuit production, exhibit very low loss at high frequencies. Previous results are confirmed in that JFET chips encapsulated with ceramic headers (under production conditions) produce significantly lower noise than epoxy or glass encapsulated JFETs. For a 2-?sec main amplifier Gaussian shaping time, the high purity A12O3; flat substrates produce less noise than the BeO headers. For 5-?sec shaping, no significant difference is observed between the two ceramic materials.