There's a ton of road maps and technology initiatives for next-generation discrete power MOSFETs in desktop, portable and automotive applications, but at their core, most of them leave manufacturers with just two ways to go. Vendors can deliver significantly better device characteristics in roughly the same size package, or they can deliver equal or incrementally better performance in something somewhat smaller. As demands turn increasingly to application-specific devices and how well they perform per unit of printed-circuit board real estate, from the chip maker's perspective, the focus is on the second option for both n- and p-channel devices.
Indeed, a snapshot of activity shows devices with higher voltage- and current-handling capability as various trench technologies are optimized. Also, more innovative packages maximize device efficiency. And the first packageless chip technology specifically touted for power MOSFETs has arrived.
From the user's standpoint, the result of these developments, more than ever before, is to migrate to an objective-based goal built on the need for higher chip densities. It's less concerned with the specific merits per se of planar vs. trench technology or the related and contentious arguments pitting on-resistance against gate charge. Or the arguments concerning IGBTs vs. MOSFETs. It's more concerned with what the power technologies actually achieve in specific topologies.
From large-signal n-channel types for dc/dc converters to smaller-signal p-channel devices for load switching in portables, application-specific MOSFET families form the basis of a good number of product lines today. First conceived as "matched" n and p pairs for "standard design" converters, they've expanded to standard, optimal and benchmark-grade levels whose n and p members can be independently selected.
At present there are three general levels of partitioning: under 40 volts or so for battery management and dc/dc converters, 40 to 200 V (dc/dc converters, uninterruptible power supplies, automotives) and above 200 V for switched-mode supplies, industrial motor controls and electronic ballasts. The more advanced families embracing this philosophy include those from International Rectifier Inc. (El Segundo, Calif.), which recently completed the second phase of its road map. The latest introduction includes three families comprising more than 40 power semiconductors for both isolated and nonisolated dc/dc converter designs (see May 8, page 139). They include a HEXFET family for isolated dc/dc converters with sub-2-V outputs; a MOSFET chip set for nonisolated multiphase converters operating at above 1 MHz; and a dual FETKY device for synchronous buck converters such as those used in portable devices. The family will ultimately address component and packaging technology for powering advanced microprocessors at 1 V and below.
Other notable offerings at the low-voltage end, where recent activity has set a furious pace, include those from Intersil Inc. (Palm Bay, Fla.), which touts the 30-V n-channel MOSFETs in its Dense Trench family as a breakthrough for low-voltage, high-efficiency operation. "By increasing channel density within the cell structure of the switching MOSFET with more transistors in parallel, we can significantly improve power efficiency," said Russ Morcom, vice president and general manager of discrete power products. This technique is said to reduce specific resistance down to 0.18 milliohm/centimeter2. The first of the products start sampling this month. Intersil hopes to improve the ratio of active die to given footprint by one and a half to four times within a year.
There are other techniques for improving performance. For instance, STMicroelectronics (Lexington, Mass.) recently launched its second-generation of StripFET devices introduced two years ago in its NE series. The devices use the company's single-feature-size process in which the width of the strip is the critical parameter in MOSFET performance. In contrast, conventional power MOSFET processes depend on three cell dimensions and shrinking cell geometries, which, according to the company, leads to more complex and expensive processes. Using a special rapid thermal diffusion process, the new NF series offers a 60 percent increase in channel perimeter compared to first-generation StripFETs. This means higher current density, as well as lower gate charge. On-resistances are below 2.5 to 2.8 mohms for its n-channel STV160NF02L (20-V device) and STV160NF03L (30-V), respectively, which are suited particularly to high-efficiency dc/dc converters for telecom. There are 70 devices in the NF series, both n and p devices, rated from 20 to 100 V and with current capabilities from 2 to 160 amperes.
Similarly, at the mid-voltage levels, TrenchFET devices from Vishay (Santa Clara, Calif.) for automotive applications include the SUP and SUB families. These are devices that offer an on-resistance of 3.5 mohms for their 85-A, 40-V n-channel devices (SUP- and SUB95N04-03) and their 8-mohm, 75-A, 55-V p-channel components (SUP- and SUB75P05-08). The latter devices, they said, are useful for high-side switching applications, eliminating the traditional trade-off between performance and convenience of a MOSFET that can be driven directly by an IC.
In addition, Fairchild Semiconductor (Santa Clara, Calif.) is extending its PowerTrench technology to 200 V. Fairchild touts its new n-channel PowerTrench MOSFETs for telecom (in the FDSx570 and -670 lines) as the fastest of any similarly rated MOSFET. The trench open-cell process, according to the company, reduces gate charge by 20 percent from planar MOSFETs and also achieves as much as a 30 percent reduction in on-resistance.
The merits of the device technology are but half the story, with packaging concerns now taking up the slack. "Driving the silicon side hard, we've arrived at the law of diminishing returns," said John Trice, marketing manager for the MOS Power Products Division at ON Semiconductor (Phoenix). "The next most significant gains in lowering on-resistance will be coming from the package."
Indeed, with improvements in silicon technology, the package now accounts for as much as 40 percent of the device's on-resistance, leading to product strategies focusing largely on the packaging structure and layout.
The idea is to secure more usable dice and effectively increase cell densities. An integral part of that is lowering the effective resistance of die attachments with bump connections in place of wire bonds and the use of multiple wires in parallel. That cuts out wasted dice or dead package space.
Along those lines, the n-channel FDS7064A PowerTrench II from Fairchild is the first MOSFET for dc/dc converters to employ the company's Bottomless package, an SO-8 solder-bump ball-grid arrangement that shows its die on its bottom side (see May 1, page 135). That allows direct contact with the pc-board heat sink.
As a result, the device achieves low on-resistance (4 milliohms typical) and a junction-to-case thermal resistance of less than 1 degrees C/W, said to be a twentyfold improvement over existing wire-bonded devices. The technology will ultimately deliver about 60 percent more current than the same die packaged in a conventional SO-8, according to the company.
Another technique is Vishay's ChipFET, which brings leads to the bottom of the package to increase available die area. Most recently, International Rectifier has taken chip-scale packaging to the next step with its FlipFET, which is the first "die is the total package" device specifically claimed for power MOSFETs (see June 26, page 157).
IR says these components have a 100 percent silicon-to-footprint ratio. Although the upper limits of die size and related parameters are presently unknown, the chip technology represents a strong inroad to future higher-power devices.
Other new arrivals, basically small-signal devices for such tasks as battery management (on-resistances are tens of mohms to ohms), include four new p-channel 12- and 20-V HEXFETs from International Rectifier, said to provide new power-conversion efficiency standards in the TSSOP-8 package.
"Using IR's new IRF7700, -01, -02 and -50 in new or existing designs leads to smaller and more efficient products," said Jorge Llorends, technical marketing manager for portable products. "The new package style enables the designer to use a minimum footprint for the performance required." The TSSOP-8 package is about 35 percent smaller than the industry-standard SO-8.
Other small-signal MOSFET entries include five new devices in three- and six-pin SC-70 packages for load switching and driver applications from Vishay. The single and dual devices, both n- and p-channel in the Tx0206A and -AD (dual) line, offer rated operation at 2.5 V to maximize battery life.
Other components include two-channel MOSFETs from Antioch, Tenn.-based Rohm (the UM5K1N has common source pin, the UM6K1N versions are independent devices) in an ultrasmall SOT-363 package for portable electronics. The device (two 2SK3018 transistors) can be driven directly from the output of a microprocessor or other IC.
ON Semiconductor also launched the MMDF4207 in its MiniMOS for portables, a p-channel power MOSFET that the company says brings p-channel Rds(on) performance closer to that of an n-channel device
The MMDF4207 MiniMOS is a dual-power MOSFET in an SO-8 package. Earlier, ON Semi released the MMSF4205, a single p-channel version of the dual MOSFET. Typical applications include battery disconnect switches, dc/dc converters, linear regulators and low-dropout regulators.
In addition, Hitachi Semiconductor (San Jose, Calif.) has a 30-V p-channel HAT1048R MOSFET for portable power management that is touted as having the industry's lowest on-resistance in an SOP-8 surface-mount package. Its typical Rds(on) is 5.5 mohms (at 10-V drive), half that of previous company offerings. Hitachi said cell density is two and one half times greater than that of previous products.
COMPANY CONTACTS
Advanced Power Technology
(800) 522-0809
www.advancedpower.com
EETInfo No. 612
Fairchild Semiconductor
(888) 522-5372
www.powertrench.com
EETInfo No. 613
Hitachi Semiconductor
(800) 285-1601
www.hitachi.com/semiconductor
EETInfo No. 614
Infineon Technologies
(408) 501-6000
www.infineon.com
EETInfo No. 615
International Rectifier
(310) 252-7105
www.irf.com
EETInfo No. 616
Intersil Corp.
(321) 729-5973
www.intersil.com
EETInfo No. 617
ON Semiconductor
(602) 244-4195
www.onsemi.com
EETInfo No. 618
Rohm Electronics
(615) 641-2020
www.rohmelectronics.com
EETInfo No. 619
STMicroelectronics Inc.
(781) 861-2650
www.st.com
EETInfo No. 620
Vishay Siliconix
(800) 554-5565
www.siliconix.com
EETInfo No. 621
