An Ultrathin Organic Insulator for Metal-Insulator-Metal Diodes

Metal–insulator–metal (MIM) diodes have attracted much attention in recent years because of the possibility of operating at very high frequencies (HFs), well into the terahertz range, a promise first highlighted over 30 years ago. The MIM diode is a quantum device wherein a thin dielectric is sandwiched between two metal electrodes with dissimilar work functions, which cause an asymmetric electric current to flow through the dielectric with respect to the polarity of the electrodes. The asymmetry at zero bias can be further increased by maximizing the work function difference between the two electrodes. This increases the possibility for the diode to operate without the need for an externally applied bias, making it a useful component in a wide range of applications, including radio-frequency identification tags, thermal-energy harvesting, and HF detectors and mixers.

The fabrication of MIM diodes has been reported in the literature using several fabrication techniques. In this paper, the device has been fabricated using a low-cost technique where the dielectric layer consists of octadecyltrichlorosilane (OTS), an amphiphilic molecule consisting of an alkyl chain and a polar head group, commonly used to functionalize the surface of silicon dioxide (SiO2). Its thickness is essentially determined by the length of the alkyl chain, rather than process conditions, with a typical value of approximately 2 nm. An OTS layer was sandwiched between titanium and platinum, which have a work function difference of 1.4 eV thereby resulting in a strong nonlinear current–voltage (J –V) characteristic.