Enhancing the Device Performance of III-V Based Bipolar Transistors

Superior DC and RF performance are obtained using InGaP/GaInAsN and InP/GaInAs double heterojunction bipolar transistors with compositionally graded base layers. By grading the base layer energy band-gap, we achieve nearly a 100% improvement in DC current gain and as much as a 15% increase in the unity gain cutoff frequency (ft) relative to baseline constant-composition base layer devices. In InGaP/GaInAsN DHBTs, DC current gains as high as 250 and cutoff frequencies of 60 GHz are demonstrated for devices with a collector thickness of 400 nm and BVceo values of 8.4 Volts. Graded-base InP/InGaAs DHBTs with an ft of 135 GHz are also demonstrated. Estimations of the ft*BVceo figure-of-merit are used to compare performance of these devices to existing technologies

Size reduction of microstrip antenna by elevating centre of patch

A new structure of microstrip patch antenna with considerable reduction in its size and wide impedance bandwidth, with marginally degraded antenna performance, is proposed. These merits are obtained by elevating the centre of the radiating metallic patch, and thus increasing the electrical length of that patch more effectively. For the purpose of example, the proposed size-reduced antenna has been designed and tested at 3 GHz and 53% of size reduction is achieved compared with the conventional one. It showed the possibility that the non-planar antenna structure can provide new a design opportunity for compact devices.This work was supported by KOSEF under the ERC program through the MINT research centre at Dongguk University