A 10 W 2 GHz Silicon Carbide MESFET
One of the major problems facing traditional silicon and GaAs high power semiconductor devices is junction temperature. The devices’ high currents inevitably generate excessive heat that must be dissipated to keep the junction temperature within acceptable limits. However, silicon carbide (SiC), a relatively new semiconductor material for device fabrication, is ideal for these high power applications because it can withstand higher temperatures than Si or GaAs. Although this material has been used to produce blue light-emitting diodes, advances in the technology have made it possible to consider SiC for high power electronic device applications. As a result, the first of a new family of SiC devices has been designed for wireless and broadcast high power applications.
The model CRF-20010 SiC MESFET is a 10 W, 48 V power transistor that features 12 dB of linear gain at 2 GHz. The new device is based on a proprietary 48 V SiC MESFET technology that has advantages over conventional silicon- and GaAs-type devices. For example, the 48 V device eliminates the DC-to-DC converter required to utilize conventional silicon and GaAs high power devices. This reduction in circuitry yields increased reliability and efficiency and reduced cost. In addition, the high breakdown voltage of SiC and its superior thermal conductivity enable the device to operate at high power levels while still dissipating heat. Thus, an SiC chip provides more power than conventional devices in an equivalent package size. The 48 V breakdown for SiC is a major advantage whereas comparable silicon laterally diffused metal oxide semiconductor devices are limited to a drain/supply voltage of approximately 28 V and a typical GaAs MESFET can withstand only 12 V. Similarly, the SiC material’s thermal conductivity is 3.3 W/cm-K, while GaAs and silicon are 0.5 and 1.5 W/cm-K, respectively.
Because these SiC transistors operate from 48 V drain and –5 V DC (typ) supplies, the input and output impedances of the devices are different from those of GaAs MESFETs. For example, the real part of the output impedance is higher because the gate periphery for a specified output power is much lower. This makes matching to the device more convenient with the added benefit that the Q of the matching circuit is not as critical because the real impedance will be tens of ohms in SiC compared to a few ohms in GaAs. In addition, the tolerances of the component values required to match consistently to the input and output impedances are relaxed in a SiC device, making the transistor inherently more robust in a production environment.
The CRF-20010 SiC MESFET is designed to operate from 400 MHz to 2.5 GHz with a guaranteed minimum output power of 10 W at 2 GHz. The device operates from a 48 V DC supply with 50 percent efficiency and can supply 12 dB of gain while operating linear class A. Figure 1 shows the device’s output power vs. input power at 2 GHz; Figure 2 shows gain vs. output power. Efficiency vs. output power and third-order intermodulation distortion (IMD) vs. output peak-envelope-power (PEP) are shown in Figures 3 and 4 , respectively.
The device is housed in a flangeless ceramic package that is designed primarily for microstrip installation. Figure 5 shows the CRF-20010 MESFET’s package outline. The device’s input/output impedance for class A operation at 10 W (VDD = 48 V, IDQ = 300 mA) is shown in Figure 6 .
Applications for the CRF-20010 SiC MESFET include class A cellular and PCS base stations as well as in TDMA, CDMA and FM multicarrier amplifiers and other broadband, high power applications. Contact the company for availability and pricing.