Driven by the demands of portable products, LED manufacturers are conjuring up displays with lower power consumption, smaller packages, higher brightness and the flexibility to deliver greater product differentiation. OEMs are increasingly using blue and white LEDs for devices such as cell phones, PDAs and notebook computers, a trend that has led to some key improvements in the devices' luminosity, package size and voltage ratings, as well as price drops. Blue LEDs now typically sell for 15 to 20 cents each and white ones for 30 cents.
Vendors such as Agilent Technologies, Fairchild Semiconductor, Sharp Microelectronics and Toshiba America Electronic Components are among those offering light-emitting diodes in smaller and thinner packaging to save space and in three colors for customization, even as they lower the voltage levels of blue and white LEDs for cost and power consumption advantages.
"There's been a growing trend in cell phones from a standard yellow-green backlight toward blue and white LEDs, especially over the past few years," said Jovani Torres, Americas regional product manager for Agilent's Optoelectronic Products Division (Palo Alto, Calif.). "When they first came out [these LEDs] weren't very bright, and they used a lot of power. Over the past couple of years, the blue LED has become very bright, and that has solved a couple of problems."
Torres said OEMs don't need as many LEDs to backlight the keypad, reducing cost. And since the brighter products don't take as much power, battery life is longer.
Low-voltage blue LEDs, which surfaced last year, not only simplified designs but also lowered overall costs. In the past, the blue LEDs' higher forward voltage, of about 3.4 or 3.5 V, presented a challenge in battery-operated applications, where the nominal battery voltage is about 3.3 V, said P.C. Yong, vice president of the optoelectronics and visible-products division at Fairchild Semiconductor (San Jose, Calif.). That meant the LEDs couldn't be directly connected to the battery and usually required an additional driver circuit, which added cost, he said.
Last year, Fairchild launched a line of low-voltage blue LEDs that Yong calls a technology breakthrough. The line's simpler circuit design for cell phones enables customers to directly replace any LED, including green, with a low-voltage substitute. Fairchild's three new blue LEDs offer forward voltage of 3.15 V at 5 milliamps and a narrow forward-voltage range, of 2.75 to 3.15 V, for better color and brightness consistency.
Fairchild said that the right-angle QTLP610C-EB and QTLP611C-EB LEDs can be used in edge lighting for liquid-crystal displays and as status indicators in cell phones, PDAs and other electronic devices. The low-profile QTLP601C-EB is targeted for backlighting keypads, pushbutton switches and LCDs in portable products.
As end-product differentiation becomes more important in the consumer sector, LED manufacturers such as Agilent, Fairchild and Sharp have focused their new-product developments on very bright red, green and blue (RGB) LEDs. These multicolor LEDs allow designers to use the three color outputs individually or to mix them for multiple custom colors.
Last month Fairchild Semiconductor launched the first two products in a new series of RGB LEDs for backlighting, edge lighting and status indication for portable devices. The QTLP650D-RGB is a top-illuminating LED for backlighting and status indication, while the side-illuminating, right-angle QTLP614C-RGB is better suited for edge lighting LCDs, the company said. In addition to providing red, green or blue color output, both devices are capable of mixing the RGB light sources for multicolor output. They can be used with Fairchild's LED driver ICs for a full range of color and brightness control in portable electronics.
The QTLP650D-RGB in a 1210 package offers a footprint of 3.2 x 2.7 x 1.7 mm, diffused optics and a 140 degrees viewing angle for uniform light over a wide viewing range. The QTLP614C-RGB, with a 3.2 x 1 x 1.5-mm footprint, offers water-clear optics to optimize brightness and a 160 degrees viewing angle for edge-lighting LCDs.
For high-brightness output, both use aluminum indium gallium phosphide for red and InGaN for green and blue. Typical luminous intensity for the QTLP650D-RGB is 60 millicandelas for red, 130 mcd for green and 40 mcd for blue. Typical luminous intensity for the QTLP614C-RGB is 110 mcd for red, 100 mcd for green and 40 mcd for blue. They are available on tape and reel in quantities of 2,000 units/reel.
Similarly, Agilent Technologies rolled its tricolor ChipLED, which lets handset and PDA designers mix independent red, green and blue light sources. This makes it easier for OEMs to choose a color based on their application and gives them greater design flexibility, said the company. The devices can also be used as status indicators.
The tricolor surface-mount LED is new and has added a lot of functionality to PDAs, Agilent's Torres said. Instead of a blue LED light for a keypad, the tricolor LED allows the designer to generate a customized color, he said.
The ChipLEDs feature AlInGaP for red and InGaN for blue and green, to provide the highest brightness at the lowest power consumption for handhelds, said the company. Housed in Agilent's 3.2 x 2.7 x 1.1-mm H ChipLED package, the device comprises three dice in a triangular matrix along with diffused optics for a consistent spatial-radiation pattern and effective color mixing, said the company. The HSMF-C118 ChipLED is priced as low as 63 cents each in high volume. Delivery takes four weeks.
Agilent is working on 0.35-mm-thick LEDs that will allow OEMs to develop thinner cell phones and PDAs, as well as very bright, right-angle white LEDs to backlight LCDs. Torres said the brightness level for the initial right-angle LEDs will be 300 mcd at 20 mA and that subsequent products will be much brighter. The right-angle configuration will allow manufacturers to use fewer LEDs for backlighting, he said.
Sharp Microelectronics of the Americas (Camas, Wash.) has released a series of RGB superluminosity Tough and Flush (TAF) LEDs and surface-mount Chip LEDs that claim higher brightness in smaller packages. Developed for consumer electronics products, Sharp's first line of RGB TAF LEDs, using a three-die chip, offers what the company said is better color reproducibility than other full-color LEDs. The six-pin package with a 2.4-mm thickness is able to drive higher current without an increased degradation of the LED, according to Sharp. The six-pin configuration allows series connections of the LEDs as a backlight to drive colors independently at the same current to reduce power consumption, Sharp said.
The RGB TAF chip, GM5WA06260A, offers a typical luminous intensity of 1,725 mcd for white. Typical forward voltage is 2.3 V for red, 4.4 V for green and 4.6 V for blue. The operating temperature range is -30 degrees C to 85 degrees C. These devices are priced from $2 to $3 in quantities of 5,000.
Toshiba America Electronic Components Inc. (Irvine, Calif.) also offers a complete line of surface-mount LEDs in what Toshiba calls the industry's smallest package for a variety of backlighting applications including cell phones, digital cameras or PDAs, particularly for the Asian market.
Red, white and blue
- Fairchild's right-angle LEDs can be used in edge lighting for LCDs.
- Sharp's RGB surface-mount ChipLEDs offer high brightness in small packages.
- Agilent is developing thinner (0.35-mm) LEDs for cell phones and PDAs.
Agilent Technologies Inc.
Semiconductor Products Group
Sharp Microelectronics of the Americas
Toshiba America Electronic Components Inc.