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14 October 2008


Microsemi launches record-power SiC RF transistors for VHF and UHF radar

Microsemi Corp of Irvine, CA, USA, which manufactures analog/mixed signal ICs and high-reliability semiconductors (mainly silicon-based), has launched its first two commercial silicon carbide (SiC) products - RF transistors for high-power VHF- and UHF-band pulsed radar applications.

The new devices are the first in a series of SiC RF power transistors designed by Microsemi's Military & Aerospace Division in Santa Clara, CA using SiC chips produced in its wafer fab in Bend, OR. Both the Bend and Santa Clara operations are formerly Advanced Power Technology Inc (APT), a supplier of power semiconductors focusing on the high-power, high-speed segment of the market for RF, microwave, linear, and switchmode applications, before Microsemi acquired it in early 2006 for $169m, along with SiC technology transferred from Northrop Grumman earlier that year. Previously, in February 2006, APT licensed from US defense contractor Northrop Grumman's Electronics Systems (NGES) division SiC technology including patents and manufacturing methods allowing it to manufacture proprietary SiC microelectronic devices.

Mike Mallinger, Microsemi's director of business development for wide-bandgap products, says that the new SiC products use new chip design and processing enhancements to offer high power as well as small transistor and circuit size with 300 microsecond pulse width and 10% long-term duty factor. The 0150SC-1250M and 0405SC-1000M common-gate, n-channel, class AB static-induction transistors (SITs) offer what are claimed to be the industry’s highest power outputs at VHF (150-160MHz) and UHF (406-450MHz) frequencies, respectively, of a minimum 1250W (typically 1400W) and 1000W (typically 1100W), with power gains of 9dB and 8dB and drain efficiencies of 60% at 155MHz and 50% at 450MHz at a bias (Vdd) of +125V. The firm says that the high operating voltage of 125V (compared to just 50V for silicon) drastically reduces power supply size and dc current demand. Also, low conducting current minimizes system noise effect.

Also, Microsemi says that typical silicon-based RF power transistor solutions offered throughout the industry, such as BJT (bipolar junction transistor) or LDMOS (laterally diffused metal oxide semiconductor) devices, must use complex push-pull circuit designs to achieve similar power levels. In contrast, the SiC RF power transistors have a single-ended design with simplified impedance matching.

In addition, the new SiC devices are fabricated with 100% gold metallization and gold wires in hermetically sealed packages (measuring a compact 0.9-inches x 0.4-inches, which is 50% smaller than the highest-power devices in BJT or LDMOS). This gives what the firm claims is the highest reliability in weather radar and long-range tracking radar applications (i.e. providing military-grade long-term reliability). The product capability at 10:1 load mismatch tolerance performance improves system yields, it adds.

The performance of the new devices demonstrates the advantages that SiC technology brings to applications in avionics, radar, and electronic warfare, says Charlie Leader, VP of Military and Aerospace business (Santa Clara, CA) of Microsemi PPG. Demonstration kits of the two new SiC RF power transistors are available. E-mail: “They also underscore the leadership position Microsemi’s Power Product Group has established in providing innovative and cost-effective solutions for the most demanding RF pulsed power applications.”

Mallinger told Semiconductor Today that, by upgrading the package technology, Microsemi aims to extend the power output capabilities of its SiC technology (e.g. increasing the power output of its UHF products from 1kW to 2kW over the next 9-12 months).

Microsemi says that, as new system designs demand substantial performance increases beyond the capabilities of silicon, it will continue to develop and bring to market high-power SiC transistors for radar applications from HF (where SiC can offer performance improvements to replace existing silicon technology, with 500W L-band products scheduled next year and 750W products for Q4/2009) through to S-band (with 150W MESFETs in development, for launch in early 2009, followed by 200W products later next year, and 300-400W devices after further packaging development).

Mallinger added that Microsemi is currently using 3-inch diameter SiC epiwafers from Cree Inc of Durham, NC. However, it is working with a ‘matrix’ of four vendors, so other SiC epiwafer suppliers will be coming on-stream as second sources. Furthermore, Microsemi hopes to transition to 4-inch substrates in the next couple of quarters, but only when the cost drops sufficiently and the defect density is low enough. Mallinger comments that the firm has been working with the US Department of Defense on material evaluation, and that 4-inch substrate quality is “getting close”.

See related item:

Microsemi’s WLAN RF power amplifier shipments surpass 75m units

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