UHF Structure with Improved Thermal Capability.
Abstract
Improved transistor-geometry designs combined with advanced wafer-processing techniques resulted in substantial reductions of thermal resistance and increased power capability of uhf and microwave transistors. The development of wafer thinning techniques and a new back-metallization system (chromium-gold) and their application to a multiple-base-cell version of a 20-watt, 1-GHz transistor (TA8694) resulted in a 66-percent reduction in thermal resistance compared to the standard-processed single-base-cell device (TA7995). RF performance was evaluated by comparing the saturated output power of standard and modified devices under cw and pulse conditions (100-microsecond pulse width, 2-percent duty cycle). The ratio of cw to pulse power is indicative of the degree of optimization of the thermal design and processing techniques. The power ratio was typically 0.85 for the TA8694 (5-cell) design compared to 0.66 for the single-cell TA7995 and 0.5 for the originally proposed TA7761 design. In addition, the utilization of a fanned bonding technique resulted in improved thermal uniformity and power sharing in the multiple-cell structure, as verified by infrared evaluations. The multiple-base-cell structure of the TA7706, a 30-watt, 400-MHz transistor, was redesigned to increase cell separation from 3.8 to 6.6 mils. Application of wafer thinning techniques and chromium-gold back-metallization resulted in a 31-percent reduction in thermal resistance when compared to the original design of the TA7706 with standard processing. The cw-to-pulse-power ratio was increased from 0.76 to 0.83. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1973
- Accession Number
- AD0908542
Entities
People
- Albert F. Chen