No abstract

We report performance of sub-0.25pm emitter-width InPflnGaAsilnP DHBTs. These are the smallest emitterwidth Ill-V devices reported to date. Measured ft'fmax performance of 406GHd423GHz is the first ever reported for a sub-0.25pm emitter-width DHBT and among the fastest for any DHBTs. With the peakf; and fmw. performance occurring at I, = 8mA (Vch-1.2Sv), this is the lowest power consumption DHBT ever reported with state of the art cutoff frequencies. The as-patterned emitter contact metal width for these devices was 0.25pm and the width of the emitter at the emitter-base junction is less than 0.25pm owing to undercutting of the underlying emitter semiconductor. When comparing with 0.4pm emitter width DHBTs, we find that 0.4pm device has the higher measured f,, 4 2 0 G H z , due to the lower emitter resistance for that emitter layout. Fmsx was highest for the 0.2Spm emitter devices due to lower hasecollector mesa capacitance, Ca, which results from the reduced mesa width. We find this behavior to be consistent with scaling tradeoffs in the design of ultra-fast DHBTs.

No abstract

The Primary Mirror of the Keck Observatory Telescope is made up of an array of 36 hexagonal mirror segments underactive control. The measurement of the relative orientations of the mirror segments is fundamental to their control. The mechanical and electronic design of the sensors used to measure these relative positions is described along with the performance of the sensors under a variety of tests. In use, the sensors will measure relative positions with a resolution of a few nanometers. This resolution and the low noise, drift and thermal sensitivity of the sensors are adequate to stabilize the primary mirror figure to the precision required for optical and infrared astronomy.