Individually detachable polymer-silicon micro-parts for vaporizable electronics

In the interest of protecting chip information, it is desirable to break apart a chip based microsystem into unusable fragments of 10-100 μm on demand. Here we report a hybrid polymer-silicon process flow and device architecture that post-processes silicon-based electronics into arrays of silicon pillars. We call this the pillar-onpolymer (PoP) process flow. The pillars can be then individually separated from the substrate through addressable thermal detachment. We use DRIE siliconetching to fabricate through-wafer trenches in the silicon substrate, and a spun-on acid-activated polypropylene carbonate (PPC) film as a vaporizable polymer to hold the individual silicon pillars. The PPC can be vaporized locally, using pillar specific Joule heating from thin-film gold resistors, to on-demand release any pillar or pillars. In this paper, we demonstrate a 3 × 3 array of 200 μm diameter silicon pillars separated by 150 μm on a 1.2×1.2 mm² die, which can be controllably detached from the substrate. With quasi-static steady state Joule heating, the power required to detach a pillar is 42.5 mW. With pulse-powered triggering, 96.7 mW is required for 5.06 seconds of heating to trigger a 0.25 mm² area of the die.