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Device Development History

Device Development History

Ultrafast Electron Devices (2) – Inauguration of MMIC Group

Reasons for MMIC Development

Hybrid ICs consist of semiconductor ICs and electronic components, such as capacitors, resistors, and coils, mounted on a substrate and integrated into a single unit. Since hybrid ICs support high density, high frequency, and better quality, we started developing these devices for measuring instruments around 1970. Hybrid ICs include thick-film types based on printing technology, and thin-film types made by vapor deposition or sputtering. They have contributed to the smaller size and higher performance of measuring instruments, as well as to higher functionality by minimizing high-frequency-signal loss. However, key semiconductor ICs were still purchased from external suppliers, causing a bottleneck in developing higher performance and functionality. Semiconductor ICs based on silicon (Si) substrates are used widely as general-purpose LSI/CPU/memory integrated circuits. Since the Si substrate is made of single element, their big advantage is that large substrates can be fabricated at low cost, making them ideal for mass production. In contrast, ICs for measuring instruments require leading-edge, high-frequency operation, which means changing the simple Si substrate to a compound substrate formed from several different semiconductors. However, compound substrates are not easily mass-produced due to high cost and difficulties in increasing wafer size due to the presence of many crystal defects. In addition, very few manufacturers develop and produce them because measuring instruments are not for mass consumption.

Semiconductor physical constants
  Thermal conductivity (10-6/K) Mobility (cm2V-1s-1) Breakdown field (MV/cm)
Si 1.3 1500 0.3
GaAs 0.55 8500 0.6
InP 0.68 5400 -
GaN 2.0 1200 2.6
4H-SiC 4.9 1000 2.8
Segregation of semiconductor materials with respect to operating frequency and output power
Segregation of semiconductor materials with respect to operating frequency and output power

On the other hand, indium phosphide (InP) and gallium arsenide (GaAs) are several times faster than silicon in terms of electron mobility (speed at which electrons move), which determines the signal processing speed required for high-frequency operation, making them suitable for manufacturing ICs for high-frequency devices. In particular, InP has a larger maximum electron velocity than GaAs at applied voltages and can be used at higher frequencies. Furthermore, compound semiconductors have excellent characteristics, such as high insulation strength and high output power, and low power consumption, depending on the material. MMIC means monolithic microwave integrated circuit and refers to ICs designed specifically for high-frequency applications, often employing compound semiconductor substrates.

The hybrid ICs in our early 2-Gbit/s pulse pattern generator and the microwave communication instruments used commercial MMIC chips. Faster and more sophisticated MMICs with operating frequencies of 10 and 40 Gbit/s became more difficult to purchase with risks of sudden discontinuation or difficulties in clarifying quality issues. Therefore, we were eager to start in-house production of MMICs but were hesitant because of the time required to start IC design and manufacturing simultaneously, and the difficulty in making major investment decisions, including running costs, and acquiring the technology. At that time, we heard about a company that had been developing and manufacturing compound semiconductors but was planning to withdraw from the market and purchased their business in 1999.

Inauguration of MMIC Group

The project started with construction of a dedicated clean room (CR) at the Atsugi Plant, making it a large-scale project starting from scratch. After the CR completion in 2000, a series of facilities, such as steppers, ion implanters, various deposition systems, and etching systems were relocated, and full-scale operation began in 2001 after confirming the performance of each facility. Manufacturing semiconductors consumes large amounts of water and organic solvents, affecting not only CR facilities but also related wastewater treatment, etc., requiring approval by relevant ministries and agencies.

Typical high-speed compound transistors include the field-effect transistor (FET) and the heterojunction bipolar transistor (HBT). The former transistor controls the current between the source and drain electrodes by controlling the gate voltage, and its advanced form is well known as the HEMT (high electron mobility transistor). The latter HBT transistor achieves high current amplification and operating frequency by using semiconductors with different band gaps. We adopted the HBT as the basic transistor and concentrated our development resources on high speed and integration, considering compatibility with production of ICs for measuring instruments requiring high-frequency operation.

Although our acquired partner had developed compound ICs, the operating frequencies were mainly in the 800-MHz to 1.5-GHz band, and they used FET transistors, so there was a large difference from the required target frequencies and transistor type for our measuring instrument ICs. Therefore, we reinforced our development of higher-performance HBTs by introducing HBT technology and hiring experienced personnel. Now that we had the basic compound semiconductor and mass-production technologies, development and IC prototyping proceeded quickly, and we soon succeeded in shipping reliable ICs to our business units. In 2003, a series of GaAs HBT MMICs, including clocks, multiplexers, and demultiplexers, appeared in Anritsu 12.5-Gbit/s measuring instruments.

Early in-house MMIC products
Early in-house MMIC products
Air Bridge and VIA Hole

The switch to operating frequencies at 40 Gbit/s and above required InP processes supporting higher speeds than GaAs and fabrication had to change to match the new systems with speedy development of etching control, ion implantation, planarization with resin materials, and many others. Additionally, higher frequencies increase the difficulty of conventional processes. New technologies were required to form VIAs (holes through the insulation layer and semiconductors to connect electrodes between wires and on the front and back surfaces) as well as for step structures to air-bridge electrodes over other electrodes for the shortest wiring. It was also more difficult to implement these individual processes simultaneously within a wafer. We solved these problems one-by-one, and MMICs using InP HBTs were used in Anritsu’s 25-Gbit/s bit error measuring instruments in 2008. Most Anritsu products since then have transitioned to the InP HBT process, and the number of MMICs in measuring instruments has continued increasing. Today, our various driver amplifiers, multiplexers, demultiplexers, clock distributers, phase shifters, O/E converters, etc., are the core devices supporting clean high-frequency waveforms in Anritsu’s measuring instruments business.

Establishment of Anritsu Devices

Our previous business in manufacturing and selling optical devices continued performing relatively well, and the prospect of in-house production of high-speed devices with the launch of the MMIC team led to expectations for improved performance in line with future increases in telecommunications demand. As a result, Anritsu Devices was established in October 2003 as a wholly owned subsidiary of Anritsu Corporation. Related divisions have been integrated to establish a device-focused business committed to development of a smart society by supplying faster devices to the growing telecommunications market.