NASA OACT Submillimeter Sensors Program

Highlights (Oct. 1 -April 1, 1994)

• The NASA OACT Submillimeter Sensors Program Team has been awarded a NASA Group Achievement Award in recognition of a highly successful and challenging research effort for the development of superconducting and semiconducting-based heterodyne receivers operating at very high frequencies.

• A Solid State Local Oscillator Workshop was held in January.

• A 2.5 THz Laser LO Workshop was held in April.

Astrophysics Applications Technical Accomplishments

• Demonstrated SIS mixer performance to 750 GHz with performance that exceeds the requirement for FIRST/SMIM. This milestone was achieved almost a year ahead of schedule.

• Observations at Caltech Submillimeter Observatory in Hawaii (observations funded by SL, SIS junctions developed under this program) in August and November using waveguide SIS receiver; HCl at 626 GHz and CS at 634 GHz observed in several interstellar sources.

• KAO flights in February and September (funded by Code SZ) of quasi-optically coupled dual slot antenna mixers (developed under this program); H218O at 547 GHz and 746 GHz and HCl at 626 GHz observed in the galactic center. Silicon substrates were used instead of quartz to increase the antenna efficiency in the forward direction by 50%.

• Demonstrated 7% tripling efficiency and as high as 750 microwatts of power at 220 GHz with BNN planar varactors in waveguide mount. Additional devices, including a quantity of BNN devices integrated with filters, have been fabricated.

• Niobium bolometric mixers were fabricated and tested at 530 GHz. Initial test demonstrated mixing for the first time with these devices at submillimeter wavelengths. Because of the much smaller parasitics, these mixers are expected to flat response to higher frequencies than SIS mixers. The major unanswered technical issues are their sensitivity and IF-bandwidth.

• Micromachining of silicon nitride coated substrates and fabrication of Nb/AlOx/Nb tunnel junctions on silicon nitride membranes has been accomplished for the development of 850 GHz waveguide mixers.

• An effort to develop normal metal tuning structures to extend the performance of Nb/AlOx/Nb based mixers beyond the Nb gap has been initiated. Preliminary normal metal microstrip resonators have been fabricated which exhibit high frequency resonances to 1 THz. Microstripline phase velocities have been measured using these structures.

• Theoretical analysis tool developed for superconducting circuits and verified with experiments between 480 and 640 GHz.

• Initiated collaboration between JPL, UCSB, and Caltech on designs for grid oscillators using the GaAs/AlAs RTD process. Major challenges include yield issues and stabilization at frequencies other than the design frequencies. Such oscillators could produce far more power than single RTD devices.

Earth Remote Sensing Applications Technical Accomplishments

• Demonstrated subharmonic mixers using planar QUID with Trx=2500K (SSB) at 215 GHz; within 25% of best whisker contacted device.

• Improved QUID (quartz substrate upside-down integrated device) diode fringing capacitance from 40 fF to 10 fF using new multilayer resist process.

• Initiated collaboration with UCLA on finite difference time domain analysis

• Completed initial design for 2.5 THz slot-antenna mixer on silicon parabolic lens using Finite Difference Time Domain simulations.

• Fabricated 20 GHz scale model for 2.5 THz mixer for impedance and antenna pattern tests.