Monolithic preamplifier employing epitaxial N-channel JFETs

This paper reports the results obtained in the research program oriented to the realisation of a monolithic preamplifier for calorimetry applications at high luminosity colliders. The main purpose of the program is to arrive at a monolithic realisation with a performance as close as possible to that of discrete preamplifiers. The junction field-effect transistors employed in discrete preamplifiers have an epitaxial channel and a very heavily doped gate diffused onto it. They present the best noise and radiation tolerance characteristics. The first step in the program implementation was, accordingly, the search for a process able to make the integration of epitaxial-channel. JFETs on a monolithic substrate possible. The integration has been accomplished on the basis of a buried-layer approach to device isolation. Individual JFETs and a complete preamplifier employing only N-channel JFETs have been realised. The characterisation of the individual devices has shown that their behaviour in terms of small signal and noise parameters is very close to that of their discrete equivalents. This result, along with the very good noise performances of the preamplifier, seems to point out that the buried layer process has fulfilled the task for which it was developed