Forschungsprojekte

Resonant tunnelling diode oscillators with on-chip antenna


Khaled Arzi, Lisa Liborius, Werner Prost

Introduction

Fundamental mode free running oscillators hold the promise to provide the most compact and energy efficient chip-size sources up to THz frequencies [1]. The frequency control of free running oscillators is a major challenge possibly enabling future array-based advanced functionalities such as emission beam steering and MIMO applications [2]. The conventional approach for frequency tuning is the variation of the oscillator resonance frequency with a voltage-depended capacitance. However, any manufactural inhomogeneity affects the oscillator frequency and the voltage-controlled frequency tuning. Based on this approach it is extremely difficult to fabricate an array of oscillators emitting at the identical frequency and moreover at a pre-defined phase relation. A promising alternative is the wire-less sub-harmonic injection locking. This technique decouples the oscillator circuit from the frequency tuning element at the expense of a low-frequency sub-harmonic source. It enables a frequency tuning of an array of free running oscillators with just one tuning element.

The challenge of this proposal is to develop a compact array of oscillator/antenna circuits operating at a locked frequency with defined and stable phase conditions enabling MIMO operations. The Resonant Tunnelling Diode (RTD) offers in an ultra-wide frequency range a huge negative-differential resistance that is ideally suited to de-attenuate resonator circuits. RTD based injection locked oscillators co-integrated with on-chip antenna will be developed and fabricated in the frequency range of 0.25 THz < f < 2 THz. In this frequency range we will develop technologies for phase- and frequency locking via sub-harmonic injection.

Experiment

The oscillator used consists of a triple barrier resonant tunnelling diode (TB-RTD) integrated into a half-wavelength slot antenna. By integrating TB-RTD into an antenna, it can be used for oscillator functionality as well as a detector depending on bias condition [3,4]. At positive bias in the regime of negative differential resistance, the TB-RTD allows oscillation up to THz frequencies at room temperature. Here, we present a proof of concept for sub-harmonic frequency tuning of a free-running TB-RTD/antenna oscillator. The precise injection locking control of single oscillator is experimentally demonstrated at microwave frequencies. The fundamental mode signal peak is observed at f0 = 31.9 GHz. The peak power is about 18 dB above noise level. Next a sub-harmonic injection locking signal of fsub = f0/2 ≈ 16 GHz is applied (Fig. 1). In the whole experimental tuning range of 200 MHz the used multiplication factor N = 2 is precisely maintained while the output is pretty constant (ΔPout < +/- 0.7 dB). A higher sub-harmonic injection factor shall enable a lower sub-harmonic injection frequency (fsub = f0/4, f0/6, ...) and is therefore currently under investigation. The slot antenna used here is known for a narrow radiation bandwidth. A wider tuning capability of the output signal is expected using a bow-tie antenna [4].

Funding (2017-2019):

  • Deutsche Forschungsgemeinschaft DFG, Project C02 of the Transregional Collaborative Research Center SFB TRR 196 (MARIE) "Mobile Material Characterization and Localisation by Electromagnetic Sensing"

References

  1. T. Maekawa, H. Kanaya, S. Suzuki, M. Asada; Oscillation up to 1.92 THz in resonant tunneling diode by reduced conduction loss, Appl. Phys. Express 9:024101, 2016
  2. Y.-T. Lo, J.-F. Kiang; Comparison of Injection-Locked and Coupled Oscillator Arrays for Beamforming, IEEE Trans. Microw. Theory Techn. 63 (4), 1353-1360, 2015
  3. G. Keller, A. Tchegho, B. Münstermann, W. Prost, F.-J. Tegude, M. Suhara, "Triple Barrier Resonant Tunneling Diodes for Microwave Signal Generation and Detection", Proc. 'European Microwave Integrated Circuits Conference (EuMIC), Nürnberg, Germany, 07.10.2013
  4. M. Suhara, S. Asakawa, T. Okazaki, M. Nakamara, S. Yamashita, Y. Itagaki, M. Saito, A. Tchegho, G. Keller, A. Poloczek, W. Prost, F.-J- Tegude, "Analysis of terahertz zero bias detectors by using a triple-barrier resonant tunnelling diode integrated with self-complementary bow-tie antenna", 70th Device Research Conference (DRC), University Park TX, United States, 2012

Fig. 1. Oscillator frequency tuning via field-based sub-harmonic injection locking for N = 2.

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