Electrochemically-triggered Degradation Of Silicon Membranes For Smart On-demand Transient Electronic Devices

Transient electronics is an emerging technology that enables unique functional transformation or even physical disappearance of electronic devices after a pre-set service time or upon controllable triggering.Although silicon is the most widely-used semi-conductor material in modern electronics industry,the application of silicon into transient electronics has been greatly limited by its good chemical stability.The reported degradation acceleration mechanisms,include physical breakage of electronic substrate and chemically-accelerated dissolution,share the common disadvantages such as high risk of spurious triggering,poor stability in long time preservation,low precision control over the degradation process and poor compatibility with the existing foundry process.To address the aforementioned issues,a novel electrochemically-triggered transience mechanism of silicon-based electronics is introduced in this paper.The lithiation process would not only induce physical deformation and fracture in the silicon-based electronics but also change the chemical property of the silicon region in the electronics,ensuring the unrecoverable degradation and failure.Firstly,the mono-crystalline silicon wafer was taken as the electrode in lithium battery and the influence of experimental conditions,such as doping level in silicon and current density during discharge,on the morphology of the lithiated region was studied.The results showed a deeper lithiated region in silicon electrode when highly-doped silicon(0.005?0.01?.cm)and high current density(400?A/cm~2)were applied.Then,applying these parameters into the following experiment,the depth and components of lithiation regions in silicon as a function of time were studied.A vein-like network of Li_xSi layer was formed beneath the planar Li_xSi layer between 6?9 hours of lithiation.The morphological transformation of the Li_xSi layer greatly accelerateed the penetration of Li_xSi layer into the unlithiated Si substrate and the total thickness of lithiated region increased to be approximately 14?m.The mechanism of morphological transformation is probably originated from the formation of micro-cracks in the Si samples caused by the accumulated Li diffusion-induced stress.Finally,analytical model and finite element model were developed to reveal the evolution of diffusion-induced stress in silicon samples.The stimulation results show that maximum values of radial stress were2.80 GPa after 9 hours of lithiation and measured fracture strengths of 2?4 GPa had been reported for small Si wafer plates,indicating the stress accumulation upon lithiation for a few hours was sufficient to reach a critical point that caused silicon fracture.To further demonstrate the feasibility of applying the electrochemically-triggered transience mechanism to silicon-based electronics,silicon membrane ribbons were taken as a simplified model of silicon membrane electronics and the morphology evolution of silicon membrane ribbons was studied as a function of lithiation state.As expected,silicon membrane ribbons were fragmented into small pieces after 12 hours of lithiation.Subsequently,electrochemically-triggered degradation of silicon integrated circuit(IC)chips with metal-oxide-semiconductor field-effect transistors(MOSFETs)from a commercial 0.35?m complementary metal-oxide-semiconductor(CMOS)technology node were performed to demonstrate the potential applications for commercial electronics.The silicon IC chip was consisted of multilayer structures and its total thickness was approximately 5?m.The cross-sectional morphology of the silicon IC chips after 12 hours of lithiation suggested that the vein-like lithium affected region developed throughout the entire Si layer,indicating the complete failure of the IC chip.