Out-of-plane microwire force sensor arrays with embedded p-n diodes by selective vapor-liquid-solid growth

We proposed a concept of force sensor arrays with vertically integrated, out-of-plane, high-aspect ratio, IC-compatible silicon wires. The proposed structure gives whisker-like force sensor arrays that one end of the wire is affixed on the substrate with another end free to be touched, even though the sensing wire-element has two terminal electrodes. We fabricated the sensor array based on 3-µm-diameter, 30-µm-length p-silicon wires (1 Ω·cm) on n-silicon substrate (3–6 Ω·cm), that results in the p-n diode systems at each wire-base. When the individual wire-tip contacts with an object, the wire exhibits the change in the electrical conductance of both the p-silicon wire body and the embedded p-n diode due to the compressive force. The proposed microwire force sensor array has the possibility for numerous measurements, such as multisite contact force, shear force, surface roughness, slip, etc., with small detection area (∼20 µm
²
) and high spatial resolution (10–100 µm in pitch). This wire-based force sensor could also be used in fingertips of a robot hand that performs the grasping and the manipulating motions to handle objects.