A fully integrated, cryogenic, charge sensitive low-noise preamplifier usingn-channel JFETs and polysilicon resistors

An N-channel JFET process technology for integrated charge sensitive preamplifiers to be used with small Si(Li) and Ge(Li) X-ray detectors has been developed. The preamplifier is designed to operate at cryogenic temperatures for the best performance.;Fabrication of N-channel JFETs in an integrated charge preamplifier has been restricted due to the trade-off between process simplicity and optimal noise performance. Existing technologies require more complex isolation process steps than the standard discrete epitaxial JFET technology. This results in an increase in excess noise at low frequency as a result of processing prior to the epitaxial silicon deposition. This thesis discusses the integration of N-channel JFETs using standard epitaxial isolation technology. Because of this, the noise of the JFET can be minimized without inducing excess noise due to the integration process prior to the epitaxial silicon deposition.;The process technology allows for multiple values of pinch-off voltage JFETs on the same die. The technology also incorporates boron doped polysilicon resistors. The resistor implant dose and dimensions have been optimized to yield excess noise nearly as low as metal film resistors with the same current. The incorporation of polysilicon resistors into the process technology increases the flexibility of circuit design. The incorporation of polysilicon resistors also allows for easy integration of a small value feedback capacitor.;During the development of the low noise integrated amplifier, a new noise measurement technique referred to as the noise measurement with a charge amplifier configuration was invented. Effects of the gate current noise can be measured by the new method and the necessity of measuring the input capacitance at the operating condition is avoided, which is necessary in the conventional noise measurement method.;The prototype amplifier has a voltage gain of 520 at 150K. The equivalent input noise of the input JFET is 2.1nV/rtHz at 140K with the input capacitance of 2.1pF when the drain source voltage is 3V and the gate source voltage is 0V. Detailed characteristics of the integrated amplifier and some characteristics of the newly developed electronic reset device are presented.