Imagine glass that’s as thin as a human hair – or thinner. Ultra-thin glass, measured in micrometers (μm or microns), can be employed in a diverse range of industries and for an untold number of applications, from medical instruments to smartphones to semiconductor components.
It is now possible to produce ultra-thin glass as thin as 25 micrometers, far thinner than the industry standard of 100 microns.
SCHOTT ultra-thin glass is available in thicknesses from 25 to 210 μm. The company produces three different types of ultra-thin glass for applications with specific chemical and physical requirements. Two types of SCHOTT’s ultra-thin glass (D263® T eco and AS87) can be chemically toughened for display and touch screen applications, are scratch-resistant, and are four to ten times stronger than un-toughened glass.
The third type (AF32® eco) has a coefficient of thermal expansion equal to silicon so it’s the ideal substrate material for integrated circuit (IC) packaging in advanced electronic devices, including wearables and flexible displays. It has enormous potential to alter the course of many industries and reshape the form and function of many technologies, including integrated circuits, electronic displays, sensors, and batteries.
The science of ultra-thin glass
Even though glass is intrinsically strong, it can still shatter when enough cracks or defects are present in its surface. SCHOTT produces ultra-thin glass in large sheets through a proprietary down-draw process, which ensures the glass is produced in the tightest geometrical tolerances. Through the precisely controlled, down-draw process, molten glass is produced on rolls measuring 500 metres long; this manufacturing methods prevents surface damage and cracks and preserves the flawless glass surface.
This process produces an incredibly strong, flexible, and uniform glass between 25 and several hundred micrometers thick in tight thickness tolerances of only a few micrometers. Through chemical strengthening via an ion exchange, ultra-thin glass’s edge strength can be increased four- to ten-fold, depending on material composition and process parameters.
Tapping into electronic innovation
Ultra-thin glass shares the same coefficient of thermal expansion as silicon, a key property of AF32® eco, and has a high dimensional stability, high transmittance, low electric loss even at highest frequencies and data rates, and extremely flat and smooth surface.
By using ultra-thin glass as a substrate for IC packaging, engineers can improve reliability and reduce warpage — a critical parameter for advanced packages. Plus, IC packaging mounted on ultra-thin glass results in a lower electrical loss compared to alternatives substrates, including silicon, for high bandwidth/high frequency applications. This results in superior signal integrity and energy consumption, and consequently increased battery life. Having one material that can fulfill all of these properties is critically important as device makers push designs smaller and faster than their predecessors, and ultra-thin glass fits those needs.
When ultra-thin glass contains silicon dioxide as its main ingredient, it offers better electrical insulation in the high-frequency range than silicon. This glass, therefore, can transport data streams via so-called metallic “through glass vias” with low power dissipation and at higher speeds, including in the radio frequency range relevant for automotive radar or next-generation mobile network applications.
In advanced packaging designs, such as 2.5D and 3D, ultra-thin glass interconnects distinct semiconductor components in a cost-effective setup, optimizing the length of the electrically conductive paths. Ultra-thin glass finally covers the unmet demand for fine-structured substrates with feature sizes under the ceiling of conventional electronic substrates. The laser drilling of tiny holes, or vias, can be done with via diameters down to 20 µm and pitch length (i.e., the difference between two holes) in the same order of magnitude. Consequently, a density of more than 10.000 holes per cm² is possible.
An extension of this trend is thin-film and solid-state batteries. As a substrate, the material can withstand the high temperatures (close to 600 degrees Celsius) generated during production without sacrificing strength or shape, so engineers are opting for ultra-thin glass instead of other materials when designing batteries for wearables, Internet of Things devices, and sensors. Finally, because ultra-thin glass comes in a wide range of thicknesses, it enables further product miniaturization, so microbatteries built with ultra-thin glass can be fitted for these smaller devices.
Another property of ultra-thin glass is flexibility, which allows engineers and designers to integrate ultra-thin glass into wearable devices, curved screens, and even screens that can be rolled up. Though the material is flexible, it won’t show fatigue under repeated bending stress, e.g. when wrapped around a wrist or folded/unfolded.
In OLED display applications, ultra-thin glass prevents moisture, oxygen, and compounds from interacting with the sensitive organic compounds that make up the display. Some current OLED display technologies use plastic substrates with expensive coatings to protect the organic substances, but an ultra-thin glass substrate is perfectly hermetic by its intrinsic nature. Other properties that make it a superb replacement for plastic in these applications are a high luminous transmittance, high chemical resistance, a coefficient of thermal expansion that matches those of metals for hermetic sealings, and a smooth surface that coatings better adhere to.
A better material to touch and feel
Ultra-thin glass makes sense in touch panels and smartphone screens for these reasons. Imagine a touch panel for built-in car navigation. Ultra-thin glass would perform incredibly well in this application, as it won’t degrade or warp when exposed to the amount sunlight expected over the lifetime of an automobile, and it won’t fail or age when exposed to prolonged periods of hot or cold weather. Most importantly, ultra-thin glass still has the advantage of scratch resistance and the high-quality “touch-and-feel” impression.
Another potential application for ultra-thin glass is in touch sensors. This glass can be the final layer on the sensor, protecting it from accidental bumps. For example, ultra-thin glass improves the reliability and performance of fingerprint sensors because of its thin and extremely homogeneous profile and high dielectric constant. The glass’s thickness, its uniformity, and its high dielectric constant directly affect the sensitivity, and hence the reliability of a fingerprint sensor.
Finally, diagnostic tools can be refined by micro-sensors built with ultra-thin glass. Microfluidic cells, based on laser-structured, ultra-thin glass, can improve the accuracy of blood analysis tools in medical diagnostics while keeping costs competitive.
Thinking on the micron level
The thinner, the smaller, the stronger, the better. SCHOTT’s ultra-thin glass bends like plastic, holds up to everyday stresses, and is thinner than the coin, credit card, and dollar bill in your wallet. That’s what ultra-thin glass can do now, but its real potential lies in future applications.
Ultra-thin glass can be used in smartphone sensors, biometric scanners, health diagnostic tools, and more, including the electronics still being dreamed up. This material lets engineers imagine new design ideas for countless technologies and has the potential to jump into many different industries. By thinking on the micron level, engineers can radically transform everyday products into thinner, smaller, and better technologies. For more information, contact article author Rüdiger Sprengard, Director of New Business for SCHOTT¹s ultra-thin glass division.