Nanometer thin-film Ni–NiO–Ni diodes for detection and mixing of 30 THz radiation

Abstract

SummaryWe report on the realization and the experimental study of thin-film Ni-NiO-Ni diodes with integrated infrared antennas. These diodes are applied as detectors and mixers of 28 THz C02-laser radiation with difference frequencies up to 176 GHz. They constitute a mechanically stable alternative to the point-contact MOM diodes used today in heterodyne detection of such high frequencies. Thus, they represent the extension of present millimeter and microwaves thin-film and antenna techniques to the infrared.Our thin-film Ni-NiO-Ni diodes are fabricated on Si02/Si substrates with the help of electron-beam lithography at the IBM Research Laboratory (Rüschlikon, Switzerland).Wehave reduced the contact area to 110 nm x 110 nm in order to achieve a fast response of the device. This contact area is in the order of those of point-contact diodes and represents the smallest ever reported for thin-film MOM diodes. The thin NiO layer with a thickness of about 35 Ais deposited by sputtering. Our thin-film diodes are integrated with planar dipole, bow-tie and spiral antennas that couples the incident field to the contact.The second derivative I"(V) of the nonlinear I(V) characteristics at the bias voltage applied to the diode is measured at a frequency of 10 kHz. It determines the detection and secondorder mixing performed with the diode for frequencies from dc to at least 30 THz. The I"(V) characteristics exhibit for low bias voltage Vbias a linear dependence, which is followed by a saturation and a maximum for high Vbias. The zero-bias resistance of the diode is in the order of 100 n. It is not strictly inversely proportional to the contact area of the diode.The first application of our thin-film diodes was the detection of cw C02-laser radiation.The measured dc signal generated by the diode when illuminated with 10.6 um radiation includes a polarization-independent contribution, caused by thermal effects. This contribution is independent of the contact area and of the type of integrated antenna. The polarization-dependent contribution of the signal originates in rectification of the antenna currents in the diode by nonlinear tunneling through the thin NiO layer. It follows a cosine-squared dependence on the angle of orientation of the linear polarization, as expected from antenna theory. For the linearly polarized dipole and bow-tie antennas, the maximum detection signals are therefore measured for the polarization parallel to the antenna axis. Bow-tie antennas with a half-length of 2.3 um generate the highest detection signals. The fulllength of these antennas corresponds to 3/2 of the wavelength of the incident 10.6 um radiation in the supporting Si substrate. The relevance of the substrate wavelength confirms that our antennas are more sensitive to the radiation incident from the substrate side. The time of response of our thin-film diode is not limited by the speed of the electron-tunneling effect, but by the RC time constant of the diode circuitry. Thus, the overall best performances are attained by the diodes with ...

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