Fabrication of micro 3D sensor array with ultra-small Si wire electrodes and applications to measurement of retina cell potentials

Makoto Ishida

Ultra small Si wire probe array fabricated by VLS (Vapor-Liquid-Solid) growth on nMOS signal processing circuit has been proposed. This wire probe array can be formed on Si (111) wafers, and be used as electrodes of intelligent nerve potential sensor. Figure 1 shows the image of intelligent nerve potential sensor including Si wire probes and signal processing circuit.

Fig.1 Concept Diagram of the intelligent nerve potential sensor.

The Si wire probe with 160 mm in length and 3.5 mm in diameter at tip grown by the selective VLS growth for growth time of 2 hours at 700 ¡ëC as shown in Fig.2. The growth rate of 1 mm/min was obtained under increased Si gas conditions. The Si wire probe was fabricated on circuits after IC process as shown in Fig.3. IC circuits were coated with passivation films to protect circuit from the corrosive environment shown. Conductive of Si wire probes can be controlled using phosphorous diffusion, and resistivity of 10-2 W¡ßcm was obtained at 1100 ¡ëC diffusion. The value is low enough to use the Si wire probe for measurement of retina cell potentials. The conductive Si wire probes are encapsulated with insulating film expect the wire probe tips.

Fig.2 Selective Si wire probes of 2¡­2 array with 160 mm in length and 3.5 mm in diameter at tips by VLS growth at 700 ¡ëC for 2 hours.(66k jpeg image)

Fig.3 The Si wire probe with 30 mm in length and 2 mm in diameter at growth temperature of 600 ¡ëC for 30 min on Si (111) with W wiring circuit.(66k jpeg image)