Introduction
Microchip plays a crucial role in the semiconductor and MEMS industry, and is closely related to the development of aerospace, automotive electronics, consumer electronics, biomedicine and other fields. Nowadays, with the improvement of data security awareness, the demand for microchips with controllable lifetime is increasing. Self-destruction chip can lose its function in a way of disappearing or degrading through active or passive trigger mechanism after completing its mission. The self-destruction characteristic can prevent the leakage of chip design information, sensitive information stored on the chip, and personal privacy in electronic products. Self-destruction microchip is especially important in the military, intelligence agencies, finance, and many other government and private organizations. It also has great potential in completely eliminating the information storage modules on discarded mobile phones, computers and other electronic products.
Microchips involve inorganic or organic semiconductors, metals, packaging materials and substrate materials. A lot of research work has been devoted to the use of light, water, temperature, or electric current to trigger physical and chemical changes such as corrosion, dissolution, hydrolysis, and tearing of these materials, so as to achieve the self-destruction of microchips. There is no doubt that good results have been achieved in the previous researches on selfdestruction devices, but there are two main problems in most selfdestruction mechanisms. First, they are only suitable for microchips with special structures, which is incompatible with the existing complementary metal oxide semiconductor (CMOS) and integrated circuit (IC) manufacturing processes and technology; second, it takes a long time for these self-destruction mechanisms to fail, and some even take several years, which restricts the application of these technologies in secured hardware for protecting sensitive information or data. In order to widely realize information security and reduce the risk of data leakage, simple manufacturing process and rapid self-destruction are very important.
In this scenario, the self-destruction microchip based on energetic materials (EMs) and Au/Pt/Cr microheater has outstanding advantages. On the one hand, EMs, such as explosives, propellants and pyrotechnics, store a large amount of energy in the form of chemical energy, which can be released rapidly under external stimulation. The controllable trigger, rapid energy-release process and strong destructive property of EMs aptly meet the requirements of transient chips. Compared with traditional EMs, nano-energetic materials (nEMs) possess smaller size, faster reaction rate, and easier integration with microchips, so they are more suitable for selfdestruction microchips. On the other hand, the Au/Pt/Cr microheater itself is prepared by a MEMS-compatible micromanufacturing process, and a small current can trigger a rapid heating of the Pt resistance, so it is suitable for triggering the combustion or explosive reaction of nEMs. Therefore, we build an independent current-triggered self-destructive module by integrating Au/Pt/Cr microheater and nEMs. It can be used as an add-on module to any CMOS and IC design without requiring any specialized chip design, resorbable solutions, special substrates, or encapsulation.
Preparation of self-destruction microchip
The structure and geometric dimensions of Au/Pt/Cr microheater are determined by the numerical simulation. Then Au/Pt/Cr microheater is manufactured by MEMS technology combined with the use of photolithography technology and physical vapor deposition method. The Au, Pt and Cr layers with the geometric structure determined by the above simulation are sequentially deposited and patterned on the electrical and thermal insulation layer. A layer of photoresist is first deposited on a high thermal-resistance glass substrate, and then the deposited photoresist is patterned by high-precision photolithography; then electron beam evaporation technology is used to deposit the Au/Pt/Cr three layers; finally, high-precision photolithography technology is used to etch the gold on the specific part with gold etching solution. Figure 1a is a single Au/Pt/Cr microheater on a glass substrate with high thermal resistance. The glass substrate with high thermal resistance ensures the low energy consumption of the microheater, and the high stability of Pt/Au ensures the high reliability of the microheater.
The nEMs are integrated with the functional area of the Au/Pt/Cr microheater in the form of a thin film, and then a silicon wafer is glued on the energetic film, as shown in Figure 1b Silicon wafers are commonly used as substrates for microchips, so they can be used to verify the self-destruct effect. During the test, direct current is applied to the contact pads of the microheater through two micrometer probes, which heats the Pt resistance and triggers the combustion or explosion of the nano-energetic film, and finally destroys the silicon wafer.
Results
By applying a voltage of 20V on both contact pads of the selfdestruction microchip, the upper silicon wafer was successfully destroyed. The silicon wafer in the central area that was in direct contact with the energetic film was crushed, and the peripheral area was cracked, as shown in Figure 1c. Figure 2 is an image of the moment that the silicon wafer was crushed captured by a highspeed camera.
Figure 1 Microscopic images of a single microheater (a), microchip before selfdestruction (b), and microchip after selfdestruction (c)
Figure 2 The destructing moment of the self-destruction microchip
Reference
1.Ma, X, Gu, S, Li, Y, Lu, J, Yang, G & Zhang, K 2021, 'Additive-Free Energetic Film Based on Graphene Oxide and Nanoscale Energetic Coordination Polymer for Transient Microchip', Advanced Functional Materials, vol. 31, no. 42, 2103199.