What if rigid and solid electronics could vanish before your eyes? An emerging class of electronic devices that could physically disappear or hydrolyze has been given the name of transient electronics. The rate of dissolution depends on the material used and properties such as film thickness, polymer crystallinity, and environmental conditions. All of these parameters could be engineered to enable programmable degradation of electronic devices.
In the May issue of Advanced Materials (DOI: 10.1002/adma.201501180), a team led by Scott R. White and John A. Rogers from the University of Illinois at Urbana-Champaign report thermal-triggered degradation of electronic devices based on temperature-sensitive wax coatings that release encapsulated acid microdrop-lets. These lead to the disintegration of both the circuit and substrate. “The wax encapsulation provides a simple and versatile approach for thermally triggered device destruction, and the destruction condition is controllable by tuning wax encapsulations,” says Chan Woo Park, the lead author of this work. Above the wax melting temperature, the methanesulfonic acid that is encapsulated is released to rapidly degrade the magnesium electrodes and produce hydrogen gas. The hydrogen with methanesulfonic acid then initiates acidic depolymerization of the cyclic poly(phthalaldehyde) substrate and finally destroys the entire device.
By tuning the acid concentration, the trigger temperature, and the thickness of pure silicone wax, the researchers could adjust the transient time of simple magnesium resistors, arrays of silicon p-i-n diodes, and parallel light-emitting diode circuits with magnesium interconnect traces. Lower acid concentrations, lower trigger temperatures, and thicker wax layers all contribute to the delay of transient time. Silicone wax with different melting temperatures could also be used to tailor the trigger temperature threshold, providing another factor that gave researchers control over the structure. In addition, on-demand destruction is possible through wireless induction coupling. A self-destructive device with a Mg/SiO2/Mg resistive heater can be powered wirelessly using a magnesium inductive coil receiver to melt the wax coating and eventually lead to full device degradation.
Illustration of thermally triggered degradation of electronic devices with encapsulated acid microdroplets. Mechanisms 1 and 2 show the key degradation and depolymerization process of the magnesium electrode and substrate to achieve full disintegration. Credit: Chan Woo Park.
“The activation of transience can be made by various stimuli like bio-fluid, UV, heat, or other chemical reactions,” says Seung-Kyun Kang, an expert researcher in the field of transient electronics; “This kind of control could be useful to destroy the device on our demand to protect personal or military information. It is very closely related to hardware security applications. Also, this kind of trigger concept is very useful in the view of [a] drug release vehicle with bio-resorbable electronics as well.”
