Resonant Tunneling Diode Oscillator Research Articles

Temperature‐dependent characteristics of a RTD‐based microwave push‐push oscillator

AbstractIn this letter, the temperature dependence of a microwave push–push oscillator based on a resonant tunneling diode (RTD) has been investigated from 30°C to 80°C. An output power characteristic curve of the second‐harmonic RTD oscillator has been shifted to the higher bias voltages as temperature increases. An oscillation frequency shift of ΔfOSC has been obtained to be –9.8 MHz/K which is equivalent to the ΔfOSC of –4.9 MHz/K at the fundamental oscillation frequency of 14.45 GHz. To authors’ knowledge, this is the first report on the temperature dependent characteristics of the second‐harmonic push–push RTD oscillator.

A wide-range variable-frequency resonant tunneling diode oscillator using a variable resonator suitable for simple MEMS process

A resonant tunneling diode oscillator having a wide frequency variation range based on a novel MEMS resonator was proposed, which exploits the change in the signal propagation velocity on a coplanar waveguide according to a movable ground plane. First, we discussed the velocity modulation mechanism, and clarified the importance of the dielectric constant of the substrate. Then, a prototype device oscillating in a 10 to 20 GHz frequency range was fabricated to demonstrate the basic operation. A large and continuous increase in the oscillation frequency of about two times was achieved with this device. This is promising for various applications including THz spectroscopy.

Codesign of Compact III–V Millimeter-Wave Wavelet Transmitters With On-Chip Antennas

Monolithically integrated millimeter-wave wavelet transmitters are presented and analyzed in this paper. Two designs that include compact dielectric resonator antennas with either inductive or self-resonant input characteristics are compared. The efficient transmitter front-end core consists of a resonant tunneling diode oscillator that is quenchable by a transistor switch. A physical diode model is used to formulate small-signal matching criteria and study codesign conditions. Fabricated transmitters provide up to 11-dBm equivalent isotropically radiated power in down to 80-ps wideband wavelets at $V$ -band carrier frequencies. Analyses of the radiated waveform envelope and time-frequency characteristics give insight in the circuit operation.

Improving the peak current density of resonant tunneling diode based on InP substrate

Resonant tunneling diodes (RTD) have the potential for compact and coherent terahertz (THz) sources operating at room temperature, but their low output power severely restricts their application in THz frequency range. In this paper, two methods are adopted to increase the peak current of RTD for enhancing its output power. First, different metal contact systems (including Pt/Ti/Pt/Au and AuGe/Ni/Au) for RTD contact are introduced, and a higher current of RTD with Pt/Ti/Pt/Au contact demonstrates the superior contact characteristic of Pt/Ti/Pt/Au contact system. Second, the double barrier structure (DBS) of RTD is well designed to further improve the characteristic of RTD, and a high peak current of 154 kA/cm is achieved at room temperature. The improved peak current is very beneficial for increasing the output power of RTD oscillator.

Frequency-tunable resonant-tunneling-diode terahertz oscillators applied to absorbance measurement

We show that frequency-tunable terahertz oscillators with resonant-tunneling diodes (RTDs) can be applied to absorbance measurement, using allopurinol as a specimen, which has a characteristic absorption spectra at around 700 GHz. The RTD oscillators used in this experiment are seven elements covering from 420 to 970 GHz. The result was in good agreement with that of time-domain spectroscopy usually used in the terahertz frequency region.

Structures and Physics of Resonant Tunneling Diodes for Terahertz Oscillators

Resonant tunneling diode (RTD) is one candidate for compact and coherent room-temperature terahertz sources. In this paper, we introduce our recent results on RTD terahertz oscillators, including RTD materials and structures for high frequency oscillation. Up to now, oscillation at 1.98 THz has been achieved at room temperature. We also described structures for high output power and some applications of RTD oscillators.

Diced and grounded broadband bow‐tie antenna with tuning stub for resonant tunnelling diode terahertz oscillators

Radiation from antennas integrated with indium phosphide (InP)-based resonant tunnelling diode (RTD) oscillators is mainly through the substrate because of the effects of the large dielectric constant. Therefore, hemispherical lenses are used to extract the signal from the backside of the substrate. In this study the authors present a broadband bow-tie slot antenna with a tuning stub which is diced and mounted on a ground plane to alleviate the substrate effects. Here, the large dielectric constant substrate around the antenna conductor is removed. In addition, the ground plane underneath the diced substrate acts as a reflector and, ultimately, the antenna radiates to the air-side direction. Antenna integration with RTD oscillators is described in this study as well. Two-port bow-tie slot antennas were designed and characterised and showed the suitability of integration with power combining RTD oscillator circuits which are based on mutual coupling. The antennas were fabricated using electron beam lithography on a semi-insulating InP substrate. Simulated and measured bandwidth almost extends the entire frequency range 230–325 GHz. Simulations shows air-side radiation pattern and antenna gain of around 11 dB at 280 GHz. Simulations also show that the antenna may be fed with a 50-Ω or 30-Ω feed line, i.e. suitable feed lines, without compromising its performance which may prove beneficial for optimum loading of RTD oscillators.

Response of a resonant tunnelling diode optoelectronic oscillator coupled to a non‐linear electrical circuit

In this study, the authors present a numerical study of the dynamics of a non-linear optoelectronic oscillator (OEO) based on the resonant tunnelling diode (RTD) oscillator incorporating a photo-detector and coupled to a non-linear electrical circuit. In the first part, it is found that the RTD-OEO oscillator presents periodic and quasiperiodic behaviours depending on the values of the parameters of a pulse-like optical signal. In the second part where the RTD-OEO is coupled to the Van der Pol oscillator, the dynamics present a variety of states including bursting, relaxation and sinusoidal oscillations.

Room-Temperature Oscillation of Resonant Tunneling Diodes close to 2 THz and Their Functions for Various Applications

Compact and coherent source is a key component for various applications of the terahertz (THz) wave. We report on our recent results of THz oscillators using resonant tunneling diodes (RTDs). To achieve high-frequency oscillation, the electron delay time of RTD was reduced with a narrow quantum well and an optimized collector spacer thickness. Conduction loss at the air bridge connecting RTD and slot antenna, which works as a resonator and a radiator, was also reduced. By these structures, a fundamental oscillation up to 1.92 THz was obtained at room temperature. Theoretical calculation shows that an oscillation over 2 THz is further expected by improved structures of RTD and antenna. Using the offset slot antenna and two-element array configuration, high output power of 0.61 mW was obtained at 620 GHz. A direct intensity modulation of RTD oscillators up to 30 GHz, which is useful for high-speed wireless data transmission, was demonstrated. By the integration of a varactor diode, wide frequency sweep of 580–700 GHz in a single device and 580–900 GHz in a four-element array were also demonstrated. This result expands possible applications of RTD oscillators.

Experimental demonstration of strain detection using resonant tunneling delta‐sigma modulation sensors

AbstractA strain sensor was fabricated based on a resonant tunneling diode (RTD) oscillator. This sensor uses strain‐dependent frequency change of the RTD oscillator, and the frequency delta‐sigma modulation technique, which can convert a frequency to a digital signal with wide dynamic range and wide bandwidth. The sensor consists of an oscillator using an LC resonator and an RTD loaded on a beam of the cantilever. The cantilever was fabricated using selective wet etching of the InP substrate. In this sensor, the strain applied to the cantilever changes the current–voltage characteristics of the RTD due to the piezoelectric effect, and hence it changes the oscillation frequency. In this paper, it was demonstrated that the acoustic strain signal can be successfully detected by this sensor with noise shaping behavior, which is a unique nature of the delta‐sigma modulation.

A 1.52 THz RTD Triple-Push Oscillator With a -Level Output Power

A resonant tunneling diode (RTD)-based oscillator operating at an output operation frequency of 1.52 THz is proposed. The proposed oscillator utilizes a unique negative differential conductance characteristic and a triple-push principle for high frequency operation. The RTD triple-push oscillator with an on-chip patch antenna has been successfully fabricated by using an InP-based RTD monolithic microwave integrated circuit (MMIC) technology. The fabricated RTD oscillator shows the output power of 1.9 μW at an output frequency of 1.52 THz. The obtained DC power consumption is 11.6 mW.

Sub-terahertz and terahertz microstrip resonant-tunneling-diode oscillators

We present a theoretical analysis of traveling-wave microstrip resonant-tunneling-diode (RTD) oscillators. Such oscillators are similar to terahertz (THz) quantum-cascade lasers (QCLs) with a metal-metal waveguide and with just the active part of a single QCL period (an RTD) as their active core. Assuming realistic parameters of RTDs, we show that the microstrip RTD oscillators should be working at sub-THz and THz frequencies. Contrary to the contemporary THz QCLs, RTD microstrips are room-temperature oscillators. The major loss- and gain-enhancement mechanisms in RTD microstrips are identified.

Structure dependence of oscillation characteristics of resonant-tunneling-diode terahertz oscillators associated with intrinsic and extrinsic delay times

We investigate the effect of intrinsic and extrinsic delay times on the oscillation characteristics of resonant-tunneling-diode (RTD) terahertz oscillators. The intrinsic delay time is composed of the electron dwell time in the resonant tunneling region and the electron transit time in the collector depletion region. We obtain and discuss the structure dependence of these factors in terms of the oscillation frequency and output power measured for RTD oscillators with different quantum-well and collector-spacer thicknesses and different air-bridge widths between the RTD and a slot antenna. The highest oscillation frequency achieved in this experiment is 1.86 THz for the well and spacer thicknesses of 2.5 and 12 nm, respectively, with a 1-µm-wide air bridge. In this structure, the extrinsic delay time (80 fs) estimated from the parasitic elements is more than double the intrinsic delay time (35 fs). It is shown theoretically that an oscillation frequency of over 2 THz is possible upon the reduction in the extrinsic delay time caused by the bulk and spread resistances in RTDs.

Operation of resonant-tunneling diodes with strong back injection from the collector at frequencies up to 1.46 THz

In search for possibilities to increase the operating frequencies of resonant-tunneling diodes (RTDs), we are studying RTDs working in an unusual regime. The collector side of our diodes is so heavily doped that the collector depletion region is fully eliminated in our RTDs and the ground quantum-well subband stays immersed under (or stays close to) the collector quasi-Fermi level. The electron injection from the collector into the RTD quantum well is very strong in our diodes and stays comparable to that from the emitter in the whole range of RTD operating biases. Our RTDs exhibit well pronounced negative-differential-conductance region and peak-to-valley current ratio around 1.8. We demonstrate operation of our diodes in RTD oscillators up to 1.46 THz. We also observe a fine structure in the emission spectra of our RTD oscillators, when they are working in the regime close to the onset of oscillations.

Segregation of antiferromagnetism and high-temperature superconductivity inCa1−xLaxFe2As2

We report the effect of applied pressures on magnetic and superconducting order in single crystals of the aliovalent La-doped iron pnictide material Ca$_{1-x}$La$_{x}$Fe$_{2}$As$_{2}$. Using electrical transport, elastic neutron scattering and resonant tunnel diode oscillator measurements on samples under both quasi-hydrostatic and hydrostatic pressure conditions, we report a series of phase diagrams spanning the range of substitution concentrations for both antiferromagnetic and superconducting ground states that include pressure-tuning through the antiferromagnetic (AFM) quantum critical point. Our results indicate that the observed superconducting phase with maximum transition temperature of $T_{c}$=47 K is intrinsic to these materials, appearing only upon suppression of magnetic order by pressure tuning through the AFM critical point. In contrast to all other intermetallic iron-pnictide superconductors with the ThCr$_2$Si$_2$ structure, this superconducting phase appears to exist only exclusively from the antiferromagnetic phase in a manner similar to the oxygen- and fluorine-based iron-pnictide superconductors with the highest transition temperatures reported to date. The unusual dichotomy between lower-$T_{c}$ systems with coexistent superconductivity and magnetism and the tendency for the highest-$T_{c}$ systems to show non-coexistence provides an important insight into the distinct transition temperature limits in different members of the iron-based superconductor family.

Two-Element Tapered Slot Antenna Array for Terahertz Resonant Tunneling Diode Oscillators

Two-element tapered slot antenna (TSA) array for terahertz (THz) resonant tunneling diode (RTD) oscillators is proposed in this paper. The proposed TSA array has the advantages of both the high directivity and high gain at the horizontal direction and hence can facilitate the horizontal communication between the RTD oscillators and other integrated circuit chips. A MIM (metal-insulator-metal) stub with a T-shaped slot is used to reduce the mutual coupling between the TSA elements. The validity and feasibility of the proposed TSA array have been simulated and analyzed by the ANSYS/ANSOFT’s High Frequency Structure Simulator (HFSS). Detailed modeling approaches and theoretical analysis of the proposed TSA array have been fully addressed. The simulation results show that the mutual coupling between the TSA elements is reduced below −40 dB. Furthermore, at 500 GHz, the directivity, the gain, and the half power beam width (HPBW) at theE-plane of the proposed TSA array are 12.18 dB, 13.09 dB, and 61°, respectively. The proposed analytical method and achieved performance are very promising for the antenna array integrated with the RTD oscillators at the THz frequency and could pave the way to the design of the THz antenna array for the RTD oscillators.

28 GHz MMIC resonant tunnelling diode oscillator of around 1mW output power

Presented is a monolithic microwave integrated circuit (MMIC) resonant tunnelling diode (RTD) oscillator that employs two In0.53Ga0.47As/AlAs RTDs (5 × 5 µm2) in parallel. The oscillator works at 28.7 GHz with −0.7 dBm output power. The phase noise was −95 dBc/Hz at 100 kHz and −114 dBc/Hz at 1 MHz offset. This reported work demonstrates the potential of RTD oscillators in achieving high output power at high frequencies by utilising suitable power maximising and combining techniques.

Wireless Interrogation of an Optically Modulated Resonant Tunnelling Diode Oscillator

In this work, a resonant tunnelling diode-photo-detector based microwave oscillator is amplitude modulated using an optical signal. The modulated free running oscillator is coupled to an antenna and phase locked by a wireless carrier that allows remote extraction of the information contained in the modulation. An off-the-shelf demodulator has been used to recover the envelope of the baseband data originally contained in the optical signal. Data were successfully transmitted at a rate of 1 MSym/s with a bit error rate below 10−6. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1728–1730, 2013

High-Power Operation of Terahertz Oscillators With Resonant Tunneling Diodes Using Impedance-Matched Antennas and Array Configuration

We report the theoretical and experimental results of an examination of the structure needed to achieve high output power in resonant tunneling diode (RTD) oscillators in the terahertz range. An offset-fed slot antenna and antenna width adjustments were employed in a single oscillator to increase the output power by increasing the radiation conductance and impedance matching. A high output power oscillation (~400 μW) at 530-590 GHz was obtained by RTDs with a large negative deferential conductance (NDC) region and offset-fed slot antennas. The maximization of the output power that was obtained by adjusting the antenna width was attributed to the impedance matching between the RTD and antenna. An output power of >;1 mW is theoretically expected in an oscillator that combines an RTD with a large NDC region, offset-fed slot antenna, and antenna width adjustment. In an array configuration, oscillators with an offset structure were employed for array elements and connected together with the metal-insulator-metal stub structure. A single peak was observed in the oscillation spectrum, and combined output powers of 610, 270, and 180 μW at 620, 770, and 810 GHz were obtained in a two-element array.

Transient Schrödinger–Poisson simulations of a high-frequency resonant tunneling diode oscillator

Transient simulations of a resonant tunneling diode oscillator are presented. The semiconductor model for the diode consists of a set of time-dependent Schrödinger equations coupled to the Poisson equation for the electric potential. The one-dimensional Schrödinger equations are discretized by the finite-difference Crank–Nicolson scheme using memory-type transparent boundary conditions which model the injection of electrons from the reservoirs. This scheme is unconditionally stable and reflection-free at the boundary. An efficient recursive algorithm due to Arnold, Ehrhardt, and Sofronov is used to implement the transparent boundary conditions, enabling simulations which involve a very large number of time steps. Special care has been taken to provide a discretization of the boundary data which is completely compatible with the underlying finite-difference scheme. The transient regime between two stationary states and the self-oscillatory behavior of an oscillator circuit, containing a resonant tunneling diode, is simulated for the first time.