In microwave as well as more general areas of engineering, integration holds the key to meeting the simultaneous demands of smaller size, higher performance, and time to market. For semiconductor manufacturers, this means a continuous progression to smaller circuits. To support high-frequency applications, electronics manufacturers also must rely on a variety of process technologies and approaches. Beyond the chip itself, a plethora of process technologies exist for amplifiers and other components. Although technologies like CMOS and gallium arsenide (GaAs) continue to be viable options, process engineers are continuously developing solutions based on technologies like gallium nitride (GaN), indium phosphide (InP), and proprietary device- and circuit-level approaches.

The leading edge of chip development tends to be forged by Intel, which is why this firm’s chip strategy is so closely watched. At the International Electron Devices Meeting (IEDM) this past December, Intel announced that it had completed the development phase of its next-generation manufacturing, which shrinks chip feature sizes to 32 nm and less. The Intel 32-nm-process paper describes a logic technology that incorporates second-generation, high-dielectric-constant (k)/metal-gate technology, 193-nm immersion lithography for critical patterning layers, enhanced transistor strain techniques, and nine levels of low-k-interconnect dielectrics. The process enables the highest drive currents reported to date for 32-nm technology. NMOS saturated drive current is 1.55 mA/µm while the corresponding PMOS value is 1.21 mA/µm.

The IEDM also saw the premiere example of wafer-scale integration of InP and RF complementary-metal-oxide-semiconductor (CMOS). Despite the exceptional speed of InP transistors, dense InP integrated circuits have not been created because InP technology is much more expensive, less advanced, and harder to work with than silicon. Recently, however, researchers from HRL Laboratories integrated entire wafers of 250-nm InP double-heterostructure bipolar transistors (DHBTs) featuring transition frequency (ft) and maximum frequency of oscillation (fmax) of 300 GHz with wafers of IBM’s existing 130-nm RF-CMOS technology (commercially known as CMRF8SF).

Essentially, a partially fabricated, planar 200- or 300-mm IBM wafer is bonded to a full-thickness InP epitaxial wafer that can be either 76.2 or 100 mm in diameter. The InP wafer is temporarily bonded to a handle wafer, which allows the InP growth substrate and etch-stop layers to be removed. Next, an aluminum heat-spreader layer is deposited as a blanket film. The InP DHBT layers are then permanently bonded to the IBM CMOS wafer’s top surface.

Recently, HRL also demonstrated graphene RF field-effect transistors (FETs) as part of the Carbon Electronics for RF Applications (CERA) program (Fig. 1). These FETs are made from epitaxially grown graphene materials with on-state current of 1180 µA/µm at a drain bias of 1 V. The transistor’s RF performance, which was characterized using an HP8510 microwave vector network analyzer (VNA), yielded an extrinsic current gain cutoff frequency of 4 GHz with 2-µm gate length. An f_max of 14 GHz was achieved at Vds = 5 V. The RF speed performance is expected to be improved as the FETs are scaled to below 100-nm gate length with reduced parasitic capacitance and resistance.

While graphene FETs have been demonstrated before, most used exfoliated graphene films. In contrast, HRL demonstrated graphene FETs using epitaxial film in the RF range. The advantages of this configuration are its high current-carrying capacity, superior thermal conductivity, and low-voltage operational potential. This milestone is the first in the proposed 51-month, three-phase program to develop a new generation of carbon-based RF ICs. The goal of the effort, sponsored by the Defense Advanced Research Projects Agency (DARPA) and under the management of the Space and Naval Warfare Systems Center (SPAWAR), is to leverage graphene carbon to create components that will enable unprecedented capabilities in high-bandwidth communications, imaging, and radar systems. HRL is collaborating with a group of universities, commercial companies, and the Naval Research Laboratory (NRL) on the program.

Military funding also is behind some GaN developments at RFMD. This past November, the firm signed a $1.4 million contract with the US Department of Defense (DoD) for the development of GaN technology and high-power RF solutions. The 12-month contract, which is an extension to previous contracts with the DoD, covers goals including reliability verification, passive-element development, and technology qualification of a manufacturable 48-V GaN RF power process for amplifiers and switches. The current program also supports the demonstration of wideband, high-power GaN MMIC amplifier and switch circuits targeting L-, S-, and C-band applications.

Although Toshiba America Electronic Components or TAEC has been a steady supplier of GaAs solutions, it also has committed to the ongoing development of GaN technology as a focus area for its high-power microwave transistor line. The company’s roadmap includes additional power-added-efficiency GaAs amplifiers for satcom and microwave radios as well as a range of GaN devices for the C-, X-, Ku-, and Ka-bands. According to the company, GaN can enable higher levels of performance than GaAs, thanks to its superior material properties with higher electron velocity, higher breakdown voltage, and easier handling characteristics. The well-populated Toshiba GaN roadmap through 2010 includes devices for the C-, X-, Ku-, and Ka-bands with maximum output power of 150+ W in a C-band device. For communications applications, 4-W and 8-W C-band GaN HEMTs for wideband were planned for last year and this year followed by satcom devices including a 100+-W C-band device this year and a 150+-W C-band device in 2010.

Cree just began sampling two 120-W GaN HEMT microwave transistors for telecommunications applications like wideband code division multiple access (WCDMA), Long Term Evolution (LTE), and WiMAX. The transistors, which consist of single, input-pre-matched GaN HEMT devices, are built on high-thermal-conductivity silicon-carbide (SiC) substrates. The CGH21120F is designed to be used primarily in the 1800-to-2300-MHz frequency range while the CGH25120F is optimized for the 2300-to-2700- MHz range. When operated at 28 V, for example, the CGH21120F provides more than 110 W of peak continuous-wave (CW) power at 70 percent efficiency with gain of 16 dB. Under WCDMA 3GPP stimulus, the transistor provides 25 W average power with 40-percent efficiency in Class AB operation.

For ultra-wideband (UWB) ICs, Staccato Communications has chosen an all-CMOS approach. The most recent iteration of the Ripcord2 family is the SC4503 PCI Express wireless host controller interface for wireless Universal Serial Bus (USB) host applications. The single-chip solution integrates a WiMedia media access controller (MAC) and physical layer (PHY) together with a PCI Express interface in 65-nm CMOS technology.

Fujitsu Microelectronics America, Inc. also is focusing on 65-nm RF CMOS, as it just announced 65-nm manufacturing services. At the same time, the firm unveiled process design kits (PDKs) that are well suited for the development of systems-on-a-chip (SoCs) that integrate RF functions for Bluetooth, GPS, cellular, wireless audio/video, wireless LAN, and optical communications. Based on the Fujitsu 90- and 65-nm analog/RF CMOS process technologies, the PDKs include a comprehensive set of parameterized cells and toolkits for active and passive devices. The flexible inductor synthesis toolkit automatically generates precise and scalable inductor layout and models for high-speed analog and RF circuits.

On the handset end, Skyworks, Inc. is taking an indium- gallium-phosphide (InGaP) route to LTE. The company debuted a multiband, multimode frequency-division-duplexing (FDD)/time-division-duplexing (TDD) power amplifier this past December. By leveraging the company’s InGaP bipolar field-effect transistor (BiFET) design and Green packaging solutions, the SKY77441 supports low operating voltage down to 3 V. This fully matched, 16-pin surface-mount module was developed for LTE FDD (Band 7) and TDD (Bands 38 and 40) applications. It also covers the 2.3-to-2.7-GHz range. The SKY77441 delivers over +26 dBm of linear power output with full LTE resource-block allocation under either quadrature phase-shift keying (QPSK) or 16-state quadrature amplitude modulation (16QAM) and over +28 dBm of linear output power under WCDMA modulation.

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