Foundries Going Greener

Ultra-high voltage processes gain ground as a way to reduce cost and power in semiconductor manufacturing.

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The ongoing push towards green and energy-efficient systems is prompting the silicon foundries to jump on the bandwagon and devise their next-generation processes based on ultra-high voltage technology.

For some time, several foundries have offered 1- and 0.5-micron, ultra-high voltage processes with ratings up to 800 volts. But seeking to get a jump for the next wave of designs, the specialty foundries have taken a narrow lead in the process race over the larger players like GlobalFoundries, TSMC and UMC.

South Korea’s Dongbu HiTek and Germany’s X-Fab Silicon Foundries AG recently rolled out 0.35-micron processes with ratings at 700 volts as a means to reduce cost and power. X-Fab, for one, has moved from a 1-micron silicon-on-insulator (SOI) process to a 0.35-micron bulk technology, although the company is developing a 0.18-micron SOI scheme for 200 volt applications.

The other foundries also are working on ultra-high voltage processes at 0.35-micron and below. Ultra-high voltage processes fall into the broad category of power management and generally involve technologies from 600 volts and above. In the 600 to 800 volt segment, there is also an emerging collision course for various transistor types.

The main applications for 600 to 800 volts include AC-to-DC switching power supplies, LED lighting systems and power converters. For these systems, the market is migrating towards 0.35-micron geometries on 200mm wafers, said Thomas Hartung, vice president of marketing for X-Fab. “For analog and mixed-signal companies, we see 0.35-micron as the sweet spot,” Hartung said.

The shift towards 0.35-micron processes is expected to lower the manufacturing and product costs for systems. But the real problem has been evident for some time: How does the industry reduce or tame standby power?

In the home, for example, power supplies take AC power from a wall outlet and convert it into DC. Conventional power supplies based on older linear technology are cheap but inefficient. Appliances plugged into the wall still consume energy, or standby power, even when the product is not in use. Linear-based cell-phone chargers, for example, can consume between 0.8 to 2 Watts even when they are not connected to the phone, according to chipmaker Power Integrations Inc.

Some 5% to 15% of household electricity consumption worldwide is wasted in standby mode, according to the International Energy Agency. In the U.S. alone, standby power costs households over $5 billion in electricity a year, according to Lawrence Berkeley National Lab.

One solution to the problem is the advent of switch-mode power supplies, which are generally more efficient and expensive. For switching power supplies, the goal is to reduce costs through IC integration and finer geometries. The concept is similar for fly-back converters in LED lighting systems.

In these segments, power management chips are specified to withstand breakdown voltages at 600 volts in the event of a power surge or spike. Some vendors sell integrated power management devices at 725 volts. “You want your transistors (with ratings of at least) 600 volts to operate in the 220 AC range,” said Steve Ohr, an analyst with Gartner Inc. “You want to have tolerances at 600 volts to prevent the system from failing.”

The prevalent switching technology in these types of systems is the power MOSFET. But there are big changes within the 600 volt segment, as several transistor types are emerging in the arena. “At 600 volts, you will see a clash of the titans between a range of technologies,” Ohr said. “You will see IGBTs, bipolar, power MOSFETs, gallium-nitride (GaN) FETs, and silicon-carbide transistors.”

Foundries push ultra-high voltage
On the foundry front, there are more subtle changes taking place in the arena. In digital, most integrated device manufacturers (IDMs) have outsourced a growing percentage of their production to the foundries. In contrast, the power management IDMs tend to keep their production in-house and the foundry business is relatively smaller for high-voltage devices right now, said Robert Lineback, an analyst with IC Insights.

Still, the foundries are seeing gradual growth from an emerging crop of fabless vendors in the higher voltage segments. “For TowerJazz, 700 volts makes up approximately 20% of new power designs,” said Todd Mahlen, vice president of APAC sales and power business development for specialty foundry TowerJazz Inc. “It is a limited set of customers, compared to lower voltages. In the short term, margin numbers are better for 700 volt technology.”

The foundries do not offer a 700 volt process alone. Instead, they tend to provide a complete modular, multi-volt process, which includes low- (3.3-, 5 and 6.5 volt), medium- (20 and 30 volt) and high- and ultra-high voltage (450 and 700 volt) technologies. “6.5-, 5- and 3.3-volt are used in logic and small signal analog functions. 20 and 30 volts are ideal for gate driver voltages for high-voltage MOSFETs,” Mahlen said.

Andy Brown, vice president of foundry sales for South Korea’s MagnaChip Semiconductor, added: “People may also want 500 volts, because that is the voltage that can directly interface with an AC line. 700 volts is designed for fly-back architectures” and other systems.

Meanwhile, getting a jump on the market, Dongbu HiTek late last year claimed to offer the foundry industry’s first 700 volt process at 0.35-micron. The initial process comes without an epitaxial layer. It supports a range of voltages and maintains low on-resistance (RDSon) by using a reduced surface field technique.

Then, in May, X-Fab rolled out XU035, an 200mm, 0.35-micron process for ultra-high-voltage applications. Using bulk wafers, the process supports 20 , 40 and 700 volts with low RDSon. The total mask count ranges from 13 to 18 steps. The 0.35-micron process is ideal for integrated power-management devices, where cost and functionality are key. “The integrated solutions are becoming more and more popular,” X-Fab’s Hartung said.

Previously, X-Fab offered a 1-micron process for 650 volt applications. “That was an SOI and trench isolation architecture,” Hartung said. “But for high-volume 700 volt applications, we need bulk and 0.35-micron. It’s a cost-effective solution.”

X-Fab is developing a new 0.18-micron high-voltage process based on SOI. The applications for this process are 200 volts, which is ideal for power-over-Ethernet and ultrasound units, he said.

SOI also is getting traction in other analog and mixed-signal markets. STMicroelectronics, for example, recently rolled out a 0.16-micron, SOI-based version of its BCD process for use in medical equipment and hybrid vehicles. The process combines 1.8- and 3.3-volt logic CMOS circuits with power MOSFET transistors that can operate up to 300 volts.

“For RF, SOI is also cost-effective,” said Horacio Mendez, executive director of the SOI Industry Consortium, a group that is looking to accelerate the use of SOI in the market. In RF switch applications, SOI reduces noise and cross-talk while maintaining signal power, he said.