Resonant-Tunneling Diode Based Reflection Amplifier V. Doychinov , Dr. D.P. Steenson, H. Patel Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering University of Leeds Leeds, UK, LS2 9JT, d.p.steenson@leeds.ac.uk Abstract: This work presents a dual quantum barrier diode based 2-port reflection amplifier featuring a hybrid coupler and two resonant tunneling diodes, that have been grown and fabricated at the university of Leeds. The components used in the circuit design were chosen such that they can be realised at frequencies up to 1THz I. INTRODUCTION One of the limiting factors for sub-millimeter wave systems is the need for amplification which is presently achieved using increasingly sophisticated three terminal deep sub-micron high electron mobility transistors [3]. Furthermore, in sub-millimeter wave heterodyne receiver systems both the signal strength and the available local oscillator powers are small, and the availability of any amplification at these frequencies would make a significant impact on the availability of systems, in what has become known as the “THz gap”, due to the lack of straightforward sources and detectors in this frequency range [1, 2]. The aim of this work is to explore the design performance of a 2-port hybrid coupler based reflection amplifier, featuring quantum barrier structures based on Al (x) Ga (1-x) As:GaAs:Al (x) Ga (1-x) As material system (Fig. 1). Fig. 1. SEM of a quantum barrier resonant tunnelling diode for use at W-band. The final phase of the work will be to implement this design at both 20 GHz and 100 GHz. II. DEVICE DETAILS The diodes used were fabricated at the University of Leeds, using three separate layer structures. These are summarised briefly in Table 1. Five different device sizes were fabricated, of which the smallest two are used in this work. The sizes of the active area for these devices are 12μ m x 6μ m and 25μ m x 6μ m. We use the Negative Differential Resistance (NDR) region of the RTDs’ I-V curve for amplification. The measured DC characteristics for the three layers are presented in Fig. 2 - Fig. 4. TABLE 1. QUANTUM BARRIER LAYER DETAILS ID Barrier (nm) Al fraction Spacer layer (nm) Well (nm) L938 5 0.4 10 5 L939 1.7 1 10 5 L940 5 0.4 10 5 Fig. 2. L938 current-voltage curve Fig. 3. L939 current-voltage curve Fig. 4. L940 current-voltage curve Overall, the centre of the NDR region for layers L938 and L940 is at about ±1 V, while the L939’s is in the range of ±(2.5-4) V.