Very High-Power High-Frequency Resonant Tunnelling Diode Oscillators

We report on very high power resonant tunnelling diode (RTD) based monolithic microwave integrated circuit (MMIC) oscillators with 35 mW output power at 11 GHz and 10 mW at 49 GHz. The key to these high powers is the use of an epitaxial layer structure that give devices with large peak to valley voltage span ($\Delta$V) of 1.2 V and the use of large area devices to get large peak to valley current span ($\Delta$I). The low device self-capacitance of 0.25 fF/$\mu m^{2}$ allows the use of large area devices without limiting the maximum achievable oscillation frequency. All fabrication of the oscillator MMICs was done using low-cost photolithography techniques. The achieved power levels are unprecedented for RTD oscillators and demonstrate the very high-power capability of this technology at microwave and mm-wave frequencies, and show that it could be competitive for the next generation (6G) wireless links and automotive radar applications.

I. Introduction

Resonant tunnelling diode (RTD) technology is emerging as a suitable platform for future terahertz (THz) wireless communications and other applications [1]. RTDs are the fastest electronic devices with demonstrated frequencies of up to 1.98 THz [2] and could potentially reach beyond 4 THz with further optimisation [3]. They have been researched in cycles since the first demonstration of resonant tunnelling by Tsu and Esaki in 1973 [4], but have had limited applicability due to their low output power [4]. The latest efforts over the past decade have been underpinned by both the large interest in THz technology and applications, and the demonstrated huge THz bandwidth of RTD devices. The 0.1-3 THz frequency range, in particular, could be exploited for low-visibility imaging systems for radar/security applications, next generation ultrafast wireless communication systems, inter-chip communications, data centre communication, mobile fronthaul[backhaul applications, and spectroscopy analysis for radio astronomy research [6],[7]. In this regard, numerous reports of RTD oscillators operating in the THz range have been published [8]–[11] and now research on their use in practical systems in short range wireless communications [12],[13] and in imaging applications [14] is underway. The typical output powers reported are, however, still in the tens to hundreds of microwatts, and all these applications would benefit from more powerful milliwatt sources. Recently, utilising an active antenna array approach, a record >10mW at 450 GHz was reported [15]. Despite this impressive progress, a better understanding of the basic RTD device to maximise the RF power is still required.