SiGe CONTROL CIRCUITS Broadband SiGe Monolithic Microwave Control Circuits

T his paper reports the performance of several broadband SiGe monolithic microwave control circuits suitable for phased array radar applications. The amplitude and phase control MMICs are based on an optimized SiGe PIN diode fabricated using the IBM 5-HP SiGe foundry process. Utilizing this diode, several control circuits were designed, including a broadband (1-20 GHz) monolithic SPDT switch, a five port transfer switch, and a 6-bit phase shifter, all operating over 7-11 GHz. The IBM silicon-germanium technology permits the integration of advanced MMICs, low power VLSI digital electronics and low frequency analog circuits in a single high yield process. The availability of several high performance microwave passive and active devices on the same wafer, including SiGe HBTs, PINs and varactors, etc., makes the IBM SiGe technology an exciting paradigm for innovative circuits for RF and microwave communication systems. Fundamental to the success of any microwave control function is a high performance PIN device. The performance of the PIN is dependent on its material doping profile as well as its layout. In the IBM 5HP SiGe process, the doping profile of the PIN diode is closely linked to that of the HBT through sharing of three HBT material layers, namely, the buried N+ sub-collector layer, the N-collector layer and finally the P+ SiGe base layer. These layers have been used to form the cathode , the I-region, and the anode of the PIN diode, respectively. The material profile in IBM 5HP process is optimized for achieving a high F t HBT performance which somewhat limits its collector thickness and, consequently, the PIN's I-region thickness to approximately one-half micron. Since the material profile of the PIN is rigid due to the HBT's performance requirements, the PIN layout design should be optimized to achieve optimum microwave performance. Figure 1 shows the layout of such a vertical optimized PIN design having a square anode contact that is surrounded by a continuous cathode contact. Such a device has a periphery-to-area ratio of only 0.56, an important design factor for minimizing the device forward bias microwave resistance (R ƒ). The forward bias resistance of the PIN diode (R ƒ) is the sum of the current independent contact resistance (R c) and current dependent resistance (r ƒ), caused by the conductivity modulation of the intrinsic region. The current dependent resistance is due to the injection of the holes and electrons into the Figure 1 · SiGe vertical …