We achieved detailed characterization of resonant tunneling chaos generator circuits in microwave frequency range. The circuit is analogous to Duffing oscillator, where the third-order nonlinear potential term is emulated by the nonlinear current-voltage curve of the resonant tunneling diode. The circuit includes a periodic reset mechanism to output identical chaos signal, which is essential to observe chaos signal on a sampling oscilloscope. Though this was shown to be effective in our previous papers, the length of the waveforms to observe is limited to rather short period, and it was unclear if this technique can be used for detailed characterization of such high-frequency chaos. In this paper, we improved the circuit design to observe longer waveforms, and demonstrated that the detailed characterization is possible using this periodic resetting technique with a sampling oscilloscope. The hybrid integration scheme is also used in this paper, which allows the easiest and shortest way to mimic a circuit as per circuit design, and precise estimation of circuit parameters aiming to eliminate circuit-related abnormalities. We provide deep insight into the dynamics associated with our circuit, starting from the single period, double period, chaos, and triple period regimes, by extracting power spectra, return maps, phase portraits, and bifurcation diagrams from acquired time series using sampling oscilloscope. Our method to study microwave chaotic signals can be applied to much higher frequency ranges, such as THz frequency range.

S-parameters of InGaAs/InAlAs triple-barrier resonant tunneling diodes (TBRTDs) were measured up to 67 GHz with various mesa areas and various bias voltages. Admittance data of bare TBRTDs are deembedded and evaluated by getting rid of parasitic components with help of electromagnetic simulations for particular fabricated device structures. Admittance spectroscopy up to 67 GHz is applied for bare TBRTDs for the first time and a Kramers-Kronig relation with Lorentzian function is found to be a consistent model for the admittance especially in cases of low bias conditions. Relaxation time included in the Lorentzian function are tentatively evaluated as the order of several pico second.

A hard-type oscillator is defined as an oscillator having stable fixed points within a stable limit cycle. For resonant tunneling diode (RTD) oscillators, using hard-type configuration has a significant advantage that it can suppress spurious oscillations in a bias line. We have fabricated hard-type oscillators using an InGaAs-based RTD, and demonstrated a proper operation. Furthermore, the oscillating properties have been compared with a soft-type oscillator having a same parameters. It has been demonstrated that the same level of the phase noise can be obtained with a much smaller power consumption of approximately 1/20.

This paper theoretically presents that a terahertz (THz) oscillator using a resonant tunneling diode (RTD) and a rectangular cavity, which has previously been proposed, can radiate high output power by the impedance matching between RTD and load through metal-insulator-metal (MIM) capacitors. Based on an established equivalent-circuit model, an equation for output power has been deduced. By changing MIM capacitors, a matching point can be derived for various sizes of rectangular-cavity resonator. Simulation results show that high output power is possible by long cavity. For example, a high output power of 5 mW is expected at 1 THz.

In this paper, a compact microwave push-push oscillator based on a resonant tunneling diode (RTD) has been fabricated and demonstrated. A symmetrical spiral inductor structure has been used in order to reduce a chip area. The designed symmetric inductor is integrated into the InP-based RTD monolithic microwave integrated circuit (MMIC) technology. The circuit occupies a compact active area of 0.088 mm2 by employing symmetric inductor. The fabricated RTD oscillator shows an extremely low DC power consumption of 87 µW at an applied voltage of 0.47 V with good figure-of-merit (FOM) of -191 dBc/Hz at an oscillation frequency of 27 GHz. This is the first implementation as the RTD push-push oscillator with the symmetrical spiral inductor.

We numerically demonstrate a possibility on-off keying (OOK) type of modulation over tens gigabits per second for sub-terahertz radiation in our proposed wireless transmitter device structure towards radio over fiber (RoF) technology. The integrated device consists of an InP-based compound semiconductor resonant tunneling diode (RTD) adjacent to an InP-based photo diode (PD), a self-complementary type of bow-tie antenna (BTA), external microstrip lines. These integration structures are carefully designed to obtain robust relaxation oscillation (RO) due to the negative differential conductance (NDC) characteristic of the RTD and the nonlinearity of the NDC. Moreover, the device is designed to exhibit OOK modulation of RO due to photo current from the PD inject into the RTD. Electromagnetic simulations and nonlinear equivalent circuit model of the whole device structure are established to perform large signal analysis numerically with considerations of previously measured characteristics of the triple-barrier RTD.

Hard-type oscillators for ultrahigh frequency applications were proposed based on resonant tunneling diodes (RTDs) and a HEMT trigger circuit. The hard-type oscillators initiate oscillation only after external excitation. This is advantageous for suppressing the spurious oscillation in the bias line, which is one of the most significant problems in the RTD oscillators. We first investigated a series-connected circuit of a resistor and an RTD for constructing a hard-type oscillator. We carried out circuit simulation using the practical device parameters. It was demonstrated that the stable oscillation can be obtained for such oscillators. Next, we proposed to use series-connected RTDs for the gain block of the hard-type oscillators. The series circuits of RTDs show the negative differential resistance in very narrow regions, or no regions at all, which makes impossible to use such circuits for the conventional soft-type oscillators. However, with the trigger circuit, they can be used for hard-type oscillators. We confirmed the oscillation and the bias stability of these oscillators, and also demonstrated that the voltage swing can be easily increased by increasing the number of RTDs connected in series. This is promising method to overcome the power restriction of the RTD oscillators.

Phase locking with frequency tuning is demonstrated for a resonant-tunneling-diode terahertz oscillator integrated with a biased varactor diode. The tuning range of oscillation frequency is 606-613GHz. The phase noise in the output of the oscillator is transformed to amplitude noise, and fed back to the varactor diode together with bias voltage. The spectral linewidth at least <2Hz was obtained at the oscillation frequencies tuned by the bias voltage of the varactor diode.

In general, tunnel diodes exhibit various types of oscillation mode: the sinusoidal mode or the nonsinusoidal mode which is known as the relaxation oscillation (RO) mode. We derive a condition for generating the RO in resonant tunneling diodes (RTDs) with essential components for equivalent circuit model. A conditional equation to obtain sufficient nonlinearity towards the robust RO is clarified. Moreover, its condition also can be applied in case of a bow-tie antenna integrated RTD, thus a design policy to utilize the RO region for the antenna integrated RTD is established by numerical evaluations of time-domain large-signal nonlinear analysis towards a terahertz transmitter for broadband wireless communications.

In this study, we propose and fabricate an oscillator array composed of three resonant-tunneling-diode terahertz oscillators integrated with slot-coupled patch antennas, and which does not require a Si lens. We measure the radiation pattern for single and arrayed oscillator, and calculate the output power using the integration of the pattern. The output power of a single oscillator was found to be ～15 µW. However, using an array configuration, almost combined output power of ～55 µW was obtained.

Super regenerative detectors using a resonant tunneling diode (RTD) were fabricated and investigated for ultra-high frequency detectors. A key point is to use the RTD super regenerative detector for detecting much higher frequencies than the free-running oscillation frequency of the detector. This is possible owing to the superior high frequency characteristics of the RTDs. This has various advantages, such as circuit simplicity, easy design, and low power consumption. Clear detection of 50,GHz signal was demonstrated with a super regenerative detector which has 1.5,GHz free-running frequency. Moreover, detailed experiments revealed that the frequency dependence of the detection efficiency is smooth, and the harmonic frequencies have no effect. This is advantageous for high frequency detection.

A novel type of millimeter/submillimeter wave sampler based on resonant tunneling diodes (RTDs) was proposed, and its operation was confirmed by circuit simulation. It consists of an RTD pulse generator and an RTD detector. Owing to the fuse-like nonlinear I-V curve, highly sensitive sampling can be obtained. We also found that the effects of non-ideality in the I-V curve of the RTD can be corrected by sweeping the DC bias for the RTD detector.

Large-signal-based nonlinear models are developed to analyze a variety of dynamic performances in a resonant tunneling diode (RTD) with peripheral circuits such as an integrated broad band bow-tie antenna, a bias circuit and a bias stabilizer circuit. Dynamic modes of the RTD are classified by the time-domain analysis with the model. On the basis of our model, we suggest a possibility to discuss a terahertz order oscillation mode control, and the ASK modulation in several tens Gbit/sec in the RTD with the broad band antenna. Validity of the model and analysis is shown by explaining measured results of modulated oscillation signals in fabricated triple-barrier RTDs.

We estimated the transit time of GaInAs/AlAs double-barrier resonant tunneling diodes (RTDs) oscillating at 0.6–1 THz. The RTDs have graded emitter structures and thin barriers, and are integrated with planar slot antennas for the oscillation. The transit time across the collector depletion region was estimated from measured results of the dependence of oscillation frequency on RTD mesa area. The estimated transit time was slightly reduced with the introduction of the graded emitter, probably due to reduction of the electron transition between Γ and L bands resulted from the low electric field in the collector depletion region.

A third order harmonic oscillator has been proposed based on the resonant tunneling diode pair oscillators. This oscillator has significant advantages, good stability of the oscillation frequency against the load impedance change together with capability to output higher frequencies. Proper circuit operation has been demonstrated using circuit simulations. It has been also shown that the output frequency is stable against the load impedance change.

We derive physics-based formula of current-voltage characteristic for resonant tunneling diodes (RTDs) by using the Voigt function. The Voigt function describes the mixing condition of homogeneous and inhomogeneous broadenings of peak energy width in transmission probability, which is sensitively reflected to nonlinear negative differential resistance of RTDs. The obtained formula is applicable to the SPICE model of RTD without performing numerical integrals. We indicate validity of the formula by comparing to measured data for double-barrier and triple-barrier RTDs.

Monolithic gyrators are proposed on the basis of integrating resonant tunneling diodes (RTDs) and HEMT toward realization of broadband and high-Q passives. Feasibility of millimeter-wave active inductors using the gyrator are described with equivalent circuit analysis and numerical calculations assuming InP based RTDs and a HEMT to be integrated.

Experimental result and theoretical analysis are reported for bias-voltage dependence of oscillation frequency in resonant tunneling diodes (RTDs) integrated with slot antennas. Frequency change of 18 GHz is obtained experimentally for a device with the central oscillation frequency of 470 GHz. The observed frequency change is attributed to the bias-voltage dependence of the transit time of electrons across the RTD layers, which results in a voltage-dependent capacitance added to RTD. Theoretical analysis taking into account this transit time is in reasonable agreement with the observed results. Voltage-controlled RTD oscillators in the terahertz range are expected from the theoretical results. A structure suitable for large frequency change is also discussed briefly.

An SCFL-compatible 40-Gbit/s selector circuit using resonant tunneling diodes (RTDs) and high-electron-mobility transistors (HEMTs) is presented. The circuit comprises two monostable-bistable transition elements (MOBILEs) using RTDs, a HEMT NOR circuit, and a HEMT output buffer based on source-coupled-FET logic (SCFL). The circuit is fabricated by monolithically integrating RTDs and 0.1-µm HEMTs on an InP substrate. The fabricated circuit exhibits clear eye-opening at 40 Gbit/s with an output swing of 800 mVp-p, which is close to the conventional high-speed logic IC interface called SCFL.

Simulation of multi-band quantum transport based on a non-equilibrium Green's functions is presented in resonant tunneling diodes (RTD's), where realistic band structures and space charge effect are taken into account. To include realistic band structure, we have used a multi-band (MB) tight binding method with an sp3s* hybridization. As a result, we have found that the multiband nature significantly changes the results of conventional RTD simulations specifically for the case with indirect-gap barriers.