Development of High Breakdown Voltage InGaP/GaAs DHBTs Jiang Li 1 , Cristian Cismaru 1 , Pete Zampardi 1 , Andy Wu 1 , Eugene Babcock 1 Mike Sun 1 , Kevin Stevens 2 , and Ravi Ramanathan 1 1 Skyworks Solutions, Inc., 2427 West Hillcrest Drive, Newbury Park, CA 91320 2 Kopin Corporation, 695 Myles Standish Blvd., Taunton, MA 02780 E5mail: Jiang.li@skyworksinc.com , Phone: (805) 48054442 Keywords: InGaP, GaAs, High breakdown, DHBT Abstract In this paper, we report the development of a high breakdown voltage InGaP/GaAs HBT process for low$to$mid power and high$voltage power amplifier operation. To achieve the high$breakdown InGaP HBT, two different collector designs and collector$etch processes were investigated. The first device process approach uses a thick GaAs collector with low n $ doping. The process challenges and considerations of this long collector approach are briefly discussed. An alternative approach uses wide band gap InGaP material as part of the collector design. High breakdown voltage can be obtained from both material design approaches. However, to fully leverage the existing process modules of our high volume HBT production line and allow the re$use of our current HBT design rules and libraries, our high voltage HBT (HV$HBT) development efforts focus on HBTs with InGaP in the collector (either composite collector, CCHBT, or double heterojunctions, DHBTs). Using a slightly modified process, InGaP DHBT devices have been demonstrated with BV ceo and BV cbo values of 40 V and 56 V, respectively. A cut off frequency,   , of 40 GHz has also been obtained at a current density of =0.3 mA/5m 2 by using this process. Preliminary circuit level performance results are also presented and discussed. INTRODUCTION In recent years InGaP/GaAs heterojunction bipolar transistors (HBTs) have been the dominant technology for wireless handset power amplifier (PA) applications due to their excellent performance, reproducibility, reliability and manufacturability. With their excellent power handling capability, good linearity and power added efficiency (PAE), InGaP/GaAs HBTs have also become a candidate for PA designs in low5to5mid power infrastructure applications currently dominated by the LDMOS or pHEMT [153]. To penetrate the low5to5mid power base station PA market, the key technical challenges for the InGaP HBTs are the high voltage operation and high breakdown voltage requirements. In this paper, we discuss the development of a new InGaP/GaAs HBTs process targeted for high voltage applications. The fabrication processes of two groups of material structures are studied and evaluated. The first group achieves high voltage performance by increasing the collector thickness and reducing the collector doping [3, 4]. Typically, 2.8 Dm or 3.0 Dm collector thickness and collector doping as low as 8x10 15 cm 53 are used. The second material group uses an InGaP double heterojunction collector (DHBT) or an InGaP/GaAs composite collector (CCHBT) [5]. High breakdown voltages are obtained from both groups. However, to take advantage of the existing InGaP related process modules in our high volume HBT production facility; this work emphasizes the development of a manufacturable InGaP DHBT (or CCHBT) process. Epi design considerations and process for InGaP DHBTs are addressed in this paper. Finally, S5parameter measurements and circuit application results are presented. CONSIDERATION AND EXPERIMENT To achieve higher breakdown voltages in InGaP HBTs, two approaches can be employed. The first one is brute force: increasing the collector thickness and reducing the collector doping. However, the penalty for using a longer collector structure is that the device topology can be more than 5 Dm in depth, presenting severe process and photo lithography challenges and, potentially, introducing reliability problems. The use of a wide5band gap material, InGaP, to form a DHBT, to replace the thicker GaAs collector layer overcomes the above topology problems and improves offset voltage, and increases power handling capability. A drawback of DHBT is that a conduction band discontinuity can be introduced at the base5collector heterojunction. Such an offset can lead to current blocking degrading both the DC and RF performance. To minimize the impact of this conduction band offset, a GaAs spacer layer/doping spike combination is inserted between the p + GaAs base and InGaP collector layers [6]. This structure effectively minimizes the spiking and results in excellent I5V characteristics. To improve transistor knee voltage (reducing the on5resistance), a composite collector structure was also investigated, which consists of a short wide band gap InGaP layer in the high5field region of the 177 CS MANTECH Conference, May 14-17, 2007, Austin, Texas, USA