Optical stepper based 150mm GaAs PHEMT for microwave and millimeter-wave MMIC applications

The gate geometry of PHEMT determines the upper limit in microwave and millimeter-wave frequencies at which the transistor can be optimally useful as amplifiers. In addition to production of 0.5 mum and 0.15 mum feature gate length PHEMT on 150 mm GaAs wafer substrate, WIN has recently developed the 0.25 mum variety targeting mmic solutions covering from below X-band to frequency as high as 60 GHz. This presentation reports on device amplification performance achieved by various gate length from 0.5 mum to 0.25 mum that are created with optical I-line stepper based photolithography. AT 10 GHz, both the 0.5 mum and 0.25 mum devices achieved 60% power-added efficiency while the later is able to provide higher output power of 900 mW/mm at 7 volt operation. This report also looks at how the higher fabrication throughput, stepper-based device approaches RF performance of the 0.15 mum device made with electron-beam based lithography. Our stepper-based device has a lower capacitance C_GD than our E-beam based 0.15 mum device due to optimization of gate formation. This provides a higher gain upto 60 GHz inspite of its slightly lower unity current gain cutoff frequency F_T, which is a result of the longer gate length. Leveraging the high gain available, it is possible to realize multi-function millimeter-wave MMIC with this stepper-base technology where the PHEMT needs to have good performance in gain, RF output power, and efficiency; and it also needs to have good low noise characteristics for LNA circuit, and low on resistance and high isolation when working as a switching device. From characterization data, we are showing here that this can be simultaneously achieved. Additionally, in order to aid versatility in circuit design, both the depletion-mode device and the enhancement mode device are fabricated. This will enable low supply power consumption, and the integration of logic and control circuits in the monolithic multi-function chip.