SCHOTT solutions no. 1/2016 > Ultra-thin glass
Photo: SCHOTT/C. Costard
Flexible, stable, and ultra-thin
Faster processors, extremely small chip packages, fingerprint sensors for smartphones – ultra-thin glass is a versatile precursor for the microelectronics of tomorrow.
Aquick test does away with the usual preconceptions that pertain to a millennia-old material: Inside a bending device, a glass sheet bends to such a great extent that you can almost wrap it around your finger, but it doesn’t break. This glass is 50 micrometers thin, about as thick as a human hair. SCHOTT can produce it as thin as 25 micrometers, while ten micrometers are already targeted in the lab. The technology group ranks among the few companies that can use advanced production and processing methods to give such ultra-thin glasses the necessary stability they require for industrial use (see text box). ”Glass can literally be continuously reinvented,” explains Dr. Rüdiger Sprengard, Director of New Business for Ultra-Thin Glass at SCHOTT. ”This allows us to use its many different properties very effectively in promising future applications such as microelectronics.” Ultra-thin glass can support the trend toward miniaturization in this important industry and enhance performance where existing substrate materials reach their limits.
Glass contains silicon dioxide as its main ingredient and offers better electrical insulation in the high frequency range than the standard semiconductor material silicon. This means it can transport the data streams that play an increasingly important role in mobile communications via metallic penetrations with low power dissipation. ”Processors made of ultra-thin glass substrates can process data up to eight times faster than was previously possible,” Dr. Sprengard says. In this case, the thinness of the glass also plays a role because the shorter the conductor paths through the substrate, the lower the energy loss and the higher the data bandwidth. These and other advantages also make glass attractive for use in chip packaging. The challenge is to connect not only various electronic components in ever smaller or flatter devices, but also subsystems such as displays, cameras, speakers and microphones in smartphones. Highly efficient packaging concepts can do so by using extremely short conductor tracks.
Photo: SCHOTT/C. Costard
In fact, modern smartphones already contain 60 to 70 such packages. The platform for these connections is usually a printed circuit board made of (insulating) plastic – generally epoxy resin – or composite materials and copper for the conductor paths. Nevertheless, their rough surfaces limit the high wiring density that will be needed in the future and complicate the photolithographic patterning of the conductor paths with ever smaller feature sizes. These types of boards also cause high energy losses with increasing signal frequencies. Furthermore, the plastic substrates can bend when they are exposed to the higher temperatures caused by increased performance in smaller packages, which increases the risk of a breakdown. By contrast, ultra-thin glass boasts excellent surface quality, high dimensional stability over a wide range of temperatures and generates significantly lower electrical losses. SCHOTT is the first to be able to use these ideal characteristics in future applications. For example, SCHOTT is working on developing energy-efficient, high-frequency components in cooperation with the Fraunhofer Institute for Reliability and Microintegration (IZM) in Berlin, and is also involved in a joint project with the Georgia Institute of Technology in the USA. In this case, prototypes of interposers were manufactured from 30-micrometer thin glass from SCHOTT. These miniature circuit boards connect microelectronic components with one another or with the motherboard like conventional printed circuit boards, but enable the highest data rates and fine rewiring and vias (vertical interconnect accesses). To achieve this, SCHOTT developers drill holes or so-called vias of only a few 10 micrometers in diameter in ultra-thin glass. State-of-the-art, highly accurate machining processes that use ultrashort pulse lasers provide the basis for this.
Ultra-thin glass from SCHOTT (left) will perform important functions in the smartphone of the future (top): as toughened cover glass in flexible OLED displays, cameras or fingerprint sensors, and as a substrate material for thin-film batteries or thermally and dimensionally stable components in processors. Photo: SCHOTT/Arndt Benedikt
SCHOTT will be looking to put its vast expertise in the area of ultra-thin glass to use in many exciting future markets, particularly for the smartphone of the future. This includes bendable or foldable displays based on organic light emitting diodes (OLEDs). Tempered and therefore scratch-resistant ultra-thin glass is also ideal for use in fingerprint sensors as a substrate or an encapsulant. These detectors for reliable identification of smartphone users are already available on the market with ultra-thin glass from SCHOTT. Thin-film batteries are yet another important field of application that deserves mention. These next generation microbatteries are capable of supplying even the smallest autonomous devices or sensors with power. They can be used in ”wearables,” e.g. display devices that can be worn like a bracelet, but especially for the ”Internet of Things.” ”In order for us to be able to realize these fascinating future trends, we are already in close contact with development and industry partners and see relevant growth potential for SCHOTT,” says Dr. Sprengard. <
Measurements performed at the Thin Glass Center of Excellence in Grünenplan (left) and material tests at the Otto SCHOTT Research Center at SCHOTT headquarters in Mainz show how strong and sturdy ultra-thin glass really is. This is tested by performing two-point bending tests (right) and long-term surface resistance tests (center), for example. Photos: SCHOTT/A. Sell
”Glass is the future material for use in chip packaging”
Interview with Dr. Michael Töpper from the Business Development team at Fraunhofer Institute for Reliability and Microintegration (IZM)
Interposers (right photo, source: SCHOTT/Arndt Benedikt) connect microelectronic components inside a much smaller space than traditional printed circuit boards (on left, photo Thinkstock). A laser can be used to drill more holes in ultra-thin glass than in conventional substrates to provide for the finest vias needed: about 12,700 on a 20 by 20 centimeter area (photos centrally, source: SCHOTT).