2. Development of Ge JFETs for Deep-Cryogenic Preamplifiers SPIE - Astronomical Telescopes and Instrumentation Hawai’i, August 2002

3. R. R. Ward and R. K. Kirschman GPD Optoelectronics Corp., Salem, New Hampshire, U.S.A. M. D. Jhabvala NASA Goddard Space Flight Center, Greenbelt, Maryland, U.S.A. R. S. Babu Ball Aerospace & Technologies Corp., Boulder, Colorado, U.S.A. D. V. Camin and V. Grassi Physics Department of the University and INFN, Milan, Italy

4. ASTRO-E Preamp Assembly ~1.2 K ~120 K ~18 K

5. The Problem Sensor at ~1 K, Preamplifier at ~100 K Long Wires –Parasitic capacitance and resistance –Microphonics –EMI pickup Heat Transfer to Sensor Extra Power Mechanical Complexity

6. A Solution A Transistor That Can Operate at ~1 K

7. A Solution A Transistor That Can Operate at ~1 K We Proposed the Ge JFET (Junction Field-Effect Transistor)

8. Technical Goals for Ge JFETs Operate at Any Temperature, ~1 – 300 K Very Low Low-Frequency Noise –Equal to best Si JFETs at optimum temp (~120 K) High Input Resistance/Low Input Current Tailorable Input Capacitance Low Power Integrable Available, Standard and Custom

9. Why Ge? Ge JFETs Operate Well to Lowest Temperatures (~1 K) Both n-Channel and p-Channel JFETs Texas Instruments Ge JFET Ge Is an Elemental Semiconductor Ge Technology Is Sufficiently Developed

10. Ge JFET Cross-Section (n-channel)

11. ~1 mm Ge JFETs

12. Conduction vs Temperature

15. DC Characteristics

16. DC Characteristics - 4 K

17. DC Characteristics

19. Noise Characteristics

20. Noise Voltage - 77 K

21. Noise Voltage vs Power - 77 K

23. Noise Voltage vs Temperature

25. Noise Voltage - 4 K

26. Summary Successfully Fabricated Ge JFETs, n- and p-Channel Provided Evaluation Ge JFETs to Potential Users DC Characteristics Good at All Temperatures down to 4 K Turn-On Threshold at 4 K (T<~20 K) Achieved Low Noise down to ~30 K Noise Higher than Desired at 4 K

27. Plans Adjust Parameters to Extend Low Noise to ~1 K Reduce Noise at All Cryogenic Temperatures –Match that of Si JFETs at higher temperature For Both n- and p-Channel