Schottky clamped MOS transistors for wireless CMOS radio frequency switch applications

The feasibility of implementing integrated radio-frequency (RF) complementary metal-oxide-semiconductor (CMOS) switches is demonstrated. The most challenging part of developing CMOS RF switches is the impact of the semiconductive nature of silicon substrates. This degrades insertion loss, limits the power handling capability of switches and may also trigger latchup in CMOS circuits due to a forward biased junction in an integrated switch when the output is mismatched.; Schottky clamped metal-oxide-semiconductor (MOS) transistors for high power RF circuit applications have been implemented in foundry CMOS processes with no process modifications. The use of Schottky clamped MOS transistors in RF switches reduces the minority carrier injection into the body of the transistors when the source/drain-to-body junctions are forward biased, and this reduces susceptibility to latchup for the surrounding CMOS circuits.; To achieve insertion loss of less than 1 dB in CMOS switches, substrate resistances associated with the transistors are minimized and junction capacitances of the transistors are reduced in order to decrease signal coupling to the substrate and thus reduce substrate loss. Through layout optimization, substrate resistances of less than 20 Ω in a 0.5-μm CMOS process using p + substrates, and substrate resistances of less than 10 Ω in a 0.18-μm CMOS process using p− substrates have been achieved. These substrate resistances are low enough to make the substrate effect on insertion loss small. In addition, bias voltages have been optimized to ensure that the transistors operate within a safe voltage region while the voltage swing required to turn on source/drain-to-body junctions is increased, and thus the power handling capability of the switch is maximized.; CMOS RF switches are demonstrated in 0.5-μm and 0.18-μm CMOS processes using 3.3-V MOS transistors. At 900 MHz, the measured insertion loss is as low as 0.5 dB which is competitive to commercially available GaAs switches. At 2.4 GHz, insertion loss is 0.8 dB which is also comparable to that of GaAs switches. The power handling capability of CMOS RF switches has been increased to 24 dBm by using impedance transformation networks. These are the first CMOS switches to have sufficient performance for ISM band applications near 900 and 2400 MHz. This dissertation work has demonstrated that it is feasible to use bulk silicon CMOS technologies to implement RF switches, which will reduce the cost of RF switches and thus reduce the cost of radios.