Investigation of Nonlinearity in RF Metal Contacts Induced by the Tunneling Effect

Nonlinearity, widely existing in passive radio frequency (RF) devices, can distort the signals in the communication system and draw increasing attention in satellite communication, 5G, and future 6G communication. The nonlinearity in RF metal contacts is theoretically and experimentally investigated in this article. First, the tunneling current and the thermionic emission current induced by the native oxide film on the metal surface are numerically calculated by exploiting the Wentzel–Kramers–Brillouin method. The spectrum characteristics of the nonlinear current are investigated and analyzed. Then, an equivalent circuit for the RF metal contact is established based on the mechanical and electric parameters as well as the surface topographic parameters. The equivalent circuit is used for nonlinearity investigation and the second/third-order harmonics are simulated. The proposed method can provide good agreement with the third-order harmonic of experiments when the input power varies from 17.5 to 27.5 dBm. The simulated results reveal that the nonlinearity can be reduced by a relatively thick oxide film, which can be used to suppress nonlinearity by intentionally introducing a thick oxide film. Our methods provide a way for RF nonlinearity analysis and design.

I. Introduction

The nonlinearity in passive devices of radio frequency (RF) circuits, which can induce passive intermodulation (PIM) when signals transmit through, becomes increasingly important in communications’ systems, especially for satellite communication, 5G, and future 6G communication [1], [2], [3], [4], [5]. Typically, the nonlinearity of metal contacts can be influenced by many factors, including material properties, the surface topographic parameters, the applied pressure, oxidation, etc. [6], [7], [8], [9], [10], which make it very challenging to comprehensively investigate the nonlinearity.