Other Devices

Metal-insulator technology lends itself to other devices, in addition to diodes, detectors, and transistors. To date, Phiar has demonstrated metal-insulator variable capacitors (varactors) and modulators.

Varactors

By manipulating MIIM barrier heights and oxide widths, Phiar has created a new device that stores charge at the interface of the two insulators, thereby creating a variable capacitor, or varactor. Figure 1 shows Phiar’s varactor design band diagram and an illustration of the charge storage phenomenon.

When voltage is applied to shift an MIIM diode from its flat-band condition to forward bias, charge can be stored in the region between the two insulators. Because the amount of charge is dependent upon the applied voltage, the device serves as a varactor. Just as with a standard capacitor, charge storage gives rise to capacitance.

Click here to see the product page on our varactors containing measured varactor performance.

Modulators

Metal-insulator devices can also be use as modulators capable of modulating a broad range of wavelengths from millimeter wave through infrared. The principle of operation for the modulator is based upon the effects of matching an antenna and load. When an antenna and load are matched the absorbed power is at a maximum, and the reflected or transmitter power is at a minimum. Alternatively, when there is significant mismatch between the antenna and load, the reflected or transmitted power increases, as seen in Figure 2.

Because an MIIM diode is highly nonlinear, its differential resistance (1/slope on a current-voltage curve) is quite different at a low voltage, say 0.3 volts and at a higher voltage, say 0.4 volts. Therefore, when the applied voltage to the diode changes, the match to the antenna changes, which modulates incoming radiation.