HIGH GAIN HIGH PO WER-ADDED-EFFICIENCY SELF-ALIGNED AlGaAs/GaAs HBTs SUITABLE FOR WIRELESS COMMUNICATION APPLICATION Pan Yang, Yan Beiping, Subrata Halder, Wang Hong, Zheng Haiqun, and Ng Geok Ing Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore zyxw 639798 Abstract This paper reports an experimental investigation of the power ,performance of self-aligned AlGaAs/GaAs HBTS. at frequency 2.5GHz, which. is of interest for wireless application. On-wafer power measurement zyxwvut on 3 pmX15 pm single-emitter HBT exhibited a 18.2dB power gain with 100 mW output power (power density of 6.7W/mm) at 1dB gain compression point with PAE of 61.4%. As compared to re-aligned approach, self- aligned device achieved power gain improvement about 2 dB on an average. I. Introduction The telecommunication and wireless communication markets demand power amplifiers having high power density, high efficiency, excellent power linearity, and compact size in the microwave applications. HBT has demonstrated itself as a good promising device for these applications. Compared to GaAs MESFET and pHEMT, HBT has the advantage of higher power density, better power linearity, small chip size and single supply voltage operation [I]. The use of HBT device, due to its high linearity, will allow circuit designer to eliminate the need for linearizers and high Q-band pass filters. Use of single polarity bias network greatly simplifies amplifier design. The reduction in weight, size and complexity will result in significantly lower production cost [2]. Some reports have presented emitter-to-base re-aligned approach to design HBTs for L-band use zyxwvutsrqp [ 1,3]. The purpose of re-aligned approach at low microwave band is to allow simpler fabrication technique and to improve process yield. On the other hand, self-aligned device has a shorter spacing between base and emitter, which is an advancement towards reduction of external base resistor and external base- collector junction capacitor (&). This in turn will lead to better microwave performance This paper presents an investigation of the power performance of self-aligned AIGaAdGaAs HBTs at 2.5GHz for improved gain and PAE performance. zyx 11. Device Design In this work, HBTs were fabricated on an epitaxial layer grown by MOCVD process. The device material layer structure consists of an In,Gal. ,As emitter contact layer, a GaAs emitter cap layer, an Alo.3G%.~As emitter layer with gradings at both side, a heavily doped p-type GaAs base layer, a GaAs collector, and a sub-collector layer. Dopants for the zy n- and p-type layer are silicon and carbon, respectively. The In,Gal,As emitter contact layer was used to achieve lower emitter contact resistance and enhance the ohmic contact stability at high power application. Single-emitter finger layout configuration was investigated. The emitter finger is 3 pm wide by 15 pm long. The base ohmic contact pattern is defined both by base-to-emitter self-aligned approach and base-to-emitter re-aligned approach for comparison purpose. For re-aligned device, the spacing between base metal contact and emitter metal contact is 1 Spm. The wet etch lateral under cut of emitter mesa is around 0.3 pm. Therefore, the total spacing between base metal contact and AlGaAs emitter edge is 1.8 pm. For self-aligned device, the spacing between base metal contact and emitter metal contact is negligible and the wet etch lateral under cut of emitter mesa is still 0.3 pm. Hence, the total spacing between base metal contact and AlGaAs emitter edge is only 0.3 pm (see Fig. 1) 0-7803-5761 -2l99l$l0.00 01 999 IEEE 646