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We manufacture thin-film Ni-NiO-Ni diodes for the detection of 10 p,m CO-laser radiation with the
aid of electron and UV lithography and sputtering techniques. The minimum dimensions are 0.4 tm.
The thickness of the oxide layers is of the order of 50 A. According to theory, the response of MOM
diodes to infrared radiation should be proportional to the second derivative d21/dV2 of dc I-V
characteristics of these diodes. However, part of the response of the MOM diodes originates in the
thermal heating by the infrared radiation. Consequently, we have measured the dc I-V characteristics
as well as the response to cw 10 .tm-CO2-laser radiation of Ni-NiO-Ni diodes at room temperature
for different orientations of the diodes with respect to the incident laser radiation and its polarisation.
For Ni-NiO-Ni diodes we have observed a cosine dependence of the signal on the angle of the
polarisation versus the antenna which represents the proper non-thermal nonlinear response of the
diode. At the moment, the coupling factor is of the order of 70.
The MOM diodes and their thin-film metal-strip antennas are attached to Si wafers. The high
refractive index of bulk Si at 10 tm wavelength diminishes thç coupling of the 10 p.m laser radiation
to the MOM-diode by the attached thin-film metal strip antenna. Therefore, we reduce the thickness of
the Si wafer on the back of the MOM diodes and their antennas to about 5p.m by etching. Thus, we
increase the transmission of the Si wafer under the metal-strip antenna and improve the antenna
performance.
Furthermore, we try to increase the sensitivity of the diodes by further reduction of their minimum
dimensions, which can be achieved by direct writing with the electron beam of the electron-beamlithography
facility at Centre Suisse d'Electronique et de Microtechnique, Neuchâtel, Switzerland.
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