Sometimes it’s good to be thin-skinned

Being thin-skinned — too sensitive, too quick to react — is a self-defeating strategy in life. But smart thin films — electronic circuits on a sticker that act as sensors and can be affixed to objects — is another version of thin-skinned altogether. They give you the desirable ability to be hypersensitive and react swiftly, transforming inanimate objects into smart devices that can sense and report real-time information about their environment and condition.

Dubbed “sticktronics,” smart thin films are just like a sticker, only with embedded high-performance electronics and sensors that “smarten up” anything to which you paste them. Sticktronics let you endow objects with a variety of desired functionality — such as the ability to sense chemical changes, temperature, humidity, as well as to harness solar energy.

The applications are unlimited. For example, the so-called “Internet of Things” (IoT) has made a massive impact in many arenas by using sensors to wirelessly connect the physical and digital worlds to extend online connectivity to physical devices and everyday objects. This lets things “talk” to one another — and to servers in the cloud — to do stuff like indicate a maintenance need, an out-of-tolerance variance in a production or performance parameter, and so on.

These peelable electronic films can be cut and pasted onto any object to achieve desired functions. (Purdue University image/Chi Hwan Lee)

Smart thin films can make this digitization more pervasive by simplifying the integration of sensors and electronics with commonplace objects such as windows, cabinets and mirrors to measure environmental factors. The films can even be used on the human body. In healthcare, sticker-like sensor patches can be attached to a patient’s skin for monitoring and detection of problems. These wearables enable companies to create thin devices that conform to different parts of the human anatomy to track levels of blood sugar, hydration, stress, and so forth.

Sticktronics can also be used in smart wound bandages to detect healing indicators. They make it simpler and less costly to create IoT sensors that can monitor elements within smart infrastructure and cities — collecting data to analyze and direct traffic and transportation, utilities, and other services. In addition Sticktronics also facilitate the fabrication of flexible, low-weight solar cells for integration into objects to provide a renewable power source.

One of our key contributions at Purdue has been a breakthrough in the sticktronics fabrication process. Like other electronic circuits, sticktronics are made on a conventional silicon wafer, allowing us to use existing nanofabrication methods. Our differentiator is that we figured out how to “delaminate,” or separate, the sticktronics layer from the wafer. In a mechanical process that is not unlike peeling peeling paint, we eliminate several manufacturing steps and their associated costs, enabling multiple reuses of the wafer to fabricate other circuits.

This environmentally friendly and defect-free delamination technique is in contrast to traditional processes, which damage the wafer so it can only be used once and sport low yields due to fabrication defects. We accomplish this in a water environment at room temperature through controlled “debonding” at the interface between the pre-fabricated thin film electronics and the silicon wafer. These now-liberated, thin-film nanoelectronics can then be pasted onto objects and devices to bestow upon them added electronic features.

We see a future where our patented technology, being commercialized through team efforts in the start-up company Omniply, can help to usher in large-scale fabrication of smart thin films for widespread use across a connected future, fusing the digital and physical worlds in practical applications such as thin-film wearables, displays, batteries, and other uses.

Dr. Chi Hwan Lee

by Chi Hwan Lee

Assistant Professor, Biomedical Engineering and Mechanical Engineering, College of Engineering, Purdue University

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