Graphene Stress Transducer-Based Thermo-Mechanically Fractured Micro Valve

This paper presents the design, analysis, and testing of a single-shot thermo-mechanically triggered micromachined micro-valve with graphene on a silicon nitride (Si
_x
N
_y
) membrane. The graphene serves as a 2-D resistive heater for producing thermo-mechanical stress, to fracture the bilayer formed between nitride and the nickel used to make electrodes. It is demonstrated that the ability of graphene to carry much higher current density per unit than metal heaters enables high thermomechanical stress to be generated. The valve is demonstrated as an enabling component of polymer substrate-based vaporizable electronics. It is used for sealing rubidium (Rb) in polymer chambers, and then triggering and exposing it to ambient air to produce heat by exothermic oxidation. This heat energy is used to vaporize the polymers. The nominal valve tested in this work is a 750 μm × 750 μm membrane of Si
_x
N
_y
. An analytical and finite-element model are presented for the valve, which agree with measured membrane peak-to-peak deflection of 4.1 μm just before fracturing, and a peak fracture stress of 395 MPa. The pulsed-power for triggering the valve is nominally 142.1 ± 13.5 mW with a trigger time of 15.4 ± 3.9 ms, resulting in a very low input trigger energy of 2.2 mJ. This trigger energy is 100× lower compared with that of previously reported single-use valves in the literature.