GaAs TUNNETT diodes oscillating at 430-655 GHz in CW fundamental mode

GaAs TUNNET diodes with 75-nm thick undoped transit-time layer and 14-nm thick n/sup +/ electric-field-inducing layer were fabricated with molecular layer epitaxy. They were oscillating in fundamental-mode metal rectangular resonant cavities of WR-1.5 (0.381 /spl times/ 0.191 mm) and WR-1.2 (0.305 /spl times/ 0.152 mm) types. Continuous wave generation of -53 dBm to -49 dBm, in the frequency range of 430-510GHz, at the bias current from 500 to 560 mA was obtained in the WR-1.5 cavity. In the WR-1.2 cavity, CW generation in the range of 571-655 GHz was obtained with the bias current changing from 460 to 540 mA. Output power was -61dBm at 655 GHz. Frequency range of CW fundamental-mode TUNNETT diodes fabricated with molecular layer epitaxy extends from 60 GHz (+13 dBm) to 655 GHz.     

Generation of Submillimeter-Wave Radiation with GaAs Tunnett Diodes and InP Gunn Devices in a Second or Higher Harmonic Mode

Efficient second-harmonic power extraction was demonstrated recently with GaAs tunnel injection transit-time (TUNNETT) diodes up to 235 GHz and with InP Gunn devices up to 325 GHz. This paper discusses the latest theoretical and experimental results from second-harmonic power extraction at submillimeter-wave frequencies and explores the potential of using power extraction at higher harmonic frequencies to generate continuous-wave radiation with significant power levels at frequencies above 325 GHz. Initial experimental results include output power levels of more than 50 μW at 356 GHz from a GaAs TUNNETT diode in a third-harmonic mode and at least 0.2–5 μW in the frequency range 400–560 GHz from InP Gunn devices in a third or higher harmonic mode. The spectral output of these submillimeter-wave sources was analyzed with a simple Fourier-transform terahertz spectrometer and, up to 426 GHz, with a spectrum analyzer and appropriate harmonic mixers. Initial experimental results from a GaAs/AlAs superlattice electronic device at D-band (110–170 GHz) and J-band (170–325 GHz) frequencies are also included.     

Mixed tunneling and avalanche mechanisms in p-n junctions and their effects on microwave transit-time devices

Analytical models of dc and small-signal characteristics for Read-type diode structures are given which incorporate both tunneling and avalanche mechanisms. A "dead-space" analysis is shown to be fundamental to accurate models of thin generation regions. Pure tunneling and pure avalanche appear as the two limiting cases of the general models. In the pure tunneling limit, the diode oscillator will operate in the tunnel transit-time (TUNNETT) mode. The TUNNETT oscillator would be attractive for low-noise and medium power and efficiency applications. For diode structures which operate between the pure TUNNETT and IMPATT modes, there exists a noise performance-output power tradeoff. Computer solutions of the analytical models, for specific diode structures and operating conditions, are given, and the results are discussed and compared with experimental results whenever possible.     

GaAs TUNNETT diodes on diamond heat sinks for 100 GHz and above

Single-drift GaAs TUNNETT diodes were mounted on diamond heat sinks for improved thermal resistance and evaluated around 100 GHz in a radial line full height waveguide cavity. The diodes were fabricated from MBE-grown material originally designed for diodes that operate in CW mode around 100 GHz on integral heat sinks. An RF output power of more than 70 mW with a corresponding DC to RF conversion efficiency of 4.9% was obtained at 105.4 GHz. This is the first successful demonstration of GaAs TUNNETT diodes mounted on diamond heat sinks. To the authors' knowledge, these DC to RF conversion efficiencies and RF power levels are the highest reported to date from TUNNETT diodes and exceed those of any single discrete device made of group III-V materials (GaAs, InP, etc.) at this frequency. Free-running TUNNETT diode oscillators exhibit clean spectra with an excellent phase noise of less than -94 dBc/Hz, measured at a frequency off-carrier of 500 kHz and an RF output power of 40 mW     

GaAs TUNNETT Diodes

The tunnel-injection-transit-time (TUNNETT) diode is operated at a high frequency and has a low-noise level compared to the IMPATT diode. The tunnel injection in a thin carrier generating region of the TUNNETT depends strongly on the electric-field intensity over 1000 kV/cm where the ionization of carriers can be neglected, leading to a higher efficiency performance than that of the IMPATT. GaAs TUNNETT diodes with p+-n and p+-n-n+ structures have been fabricated by a new LPE method (the temperature-difference method under controlled vapor pressure). The fundamental oscillation at frequencies from about 100 up to 248 GHz has been obtained from the pulse-driven p+-n-n+ diodes. This paper describes the details of the oscillation characteristics of GaAs TUNNETT diodes.     

Microwave characterization of a resistive-gate MESFET oscillator

Measurements of microwave oscillations in resistive-gate MESFET contiguous-domain oscillator devices are discussed. Oscillation frequencies in the ranges from 22 to 30 GHz and 37 to 42 GHz are observed independently of the device length, and frequency can be tuned during operation by varying the source-to-gate voltage. Evidence suggests that the observed signals are harmonics of a fundamental signal in the range from 11 to 15 GHz. While the possibility that conventional transit-time Gunn domain propagation is occurring in this frequency range cannot be ruled out, the fact that frequency is independent of channel length suggests that contiguous domains are forming, at least in the longer devices. Because of its structure, the resistive-gate MESFET oscillator can be easily incorporated into MESFET integrated circuits for MMIC (monolithic microwave integrated circuit) applications     

An analysis of wide-band transferred electron devices

The trapping conditions of a high-field domain at the anode are studied by varying doping density, applied bias voltage, and doping notch depth and width near the cathode. It is shown that the frequency band of negative conductance of the trapped-domain mode depends significantly on the doping density, and a diode having the doping density of 3 × 10¹⁵/cm³exhibits the negative conductance over the wide range from 4 GHz to 42 GHz. The upper frequency limit of the negative conductance is due to the series resistance in the low-field region and the lower limit is determined by carrier transit-time effects in high-field region. The operation mode of a trapped-domain diode will change into a traveling dipole or accumulation mode from a trapped-domain mode depending on the doping density and the operation frequency for a large-signal operation.     

High-harmonic content in trapped-plasma-mode oscillators

A waveguide-coaxial cavity has enabled efficient trapped-plasma-mode harmonic generation to be extended into the K band. A power of 2 W at 3.8% efficiency was obtained at the 12th harmonic of a 1.67 GHz fundamental. The use of a lamellar grating far-infrared interferometer with a novel gated detection system verified the presence of components up to 40 GHz, a frequency corresponding to three times the normal transit-time frequency.     

High-efficiency continuous oscillations in silicon IMPATT diodes below the transit-time frequency

C.W. room-temperature operation of silicon IMPATT diodes at the first subharmonic of the transit-time frequency has been observed in a high-efficiency mode. Efficiencies as high as 8.8% at 5GHz with 1.2 Wc.w. have been achieved with current densities no more than 1480A/cm2.     

A tunable-frequency Gunn diode fabricated by focused ion-beamimplantation

The fabrication of a planar Gunn diode in which the fundamental transit-time model oscillation frequency can be tuned over the range 6-23 GHz by varying the DC bias across the device is reported. The wide-band tunability is due to a linear doping-concentration gradient between the contacts. This lateral doping is created by implanting the device with a focused beam of silicon ions and smoothly increasing the dose from contact to contact. A Gunn diode with a uniform active region, also fabricated with the focused ion beam, displays a relatively constant oscillation frequency in the same bias range     

High-frequency oscillations of p++-n+-n-n++avalanche diodes below the transit-time cutoff

According to Read, n⁺⁺-P⁺-i-P⁺⁺diodes should oscillate at special high frequencies determined by carrier transit time in the space-charge layer. Oscillations not affected by transit time were observed with p⁺⁺-n⁺- n-n⁺⁺silicon diodes. The corresponding current-voltage characteristic revealed a negative resistance setting in at a critical current. Theoretical considerations show that one-sided avalanche injection in n⁺⁺-p⁺-p⁺⁺structures may lead to a slight negative resistance for carrier concentrations smaller than the impurity concentration and for certain widths of the depletion layer. This type of negative resistance disappears in n⁺⁺-p⁺-i-P⁺⁺structures, but with increasing injection multiplication is induced in the intrinsic layer. Therefore the carrier space-charge is reduced and a negative resistance appears at a critical current density. The onset of this second injection is an upper current limit of the Read transit-time mode. The frequency range of oscillations due to avalanche space-charge feedback generally will not be separated from the range of transit-time oscillations. Thus, it must be judged carefully which mechanism is responsible for observed high-frequency oscillations. On the other hand, space-charge feedback may give additional stability to the transit-time mode.     

Indium phosphide microwave oscillators

A detailed examination has been carried out on the characteristics of transferred electron microwave oscillators constructed from epitaxial indium phosphide. Seven slices have been used, for which the layer thicknesses varied between 5.4 and 28 µm. It is shown that the mechanism of oscillation has a transit-time dependence and that the transit velocity which emerges (1.5-2 × 10⁷cm/s) is approximately the same as the peak electron drift velocity. It is therefore concluded that propagating space-charge layers are responsible for the oscillations. However, in view of the high transit velocities involved, it is unlikely that the space-charge layers are well-formed dipolar domains. Despite the transit-time dependence, individual devices have been made to oscillate over very wide frequency ranges (8-28 GHz). Operation of devices at frequencies up to 40 GHz has established the high-frequency capability of the oscillators. The best pulsed results obtained have included 0.5 W, 6.3 percent at 13.8 GHz; 1.05 W, 4.2 percent at 18.0 GHz and 0.65 W, 2.6 percent at 25.0 GHz. Continuous operation of these diodes has not yet been possible due to material and thermal technology limitations.     

9.5 GHz GaInP/GaAs HBT divide-by-two frequency divider using super-dynamic D-type flip?flop technique

A frequency divider with super-dynamic D-type flip-flop is demonstrated in 2 mum GalnP/GaAs HBT (f_T = 40 GHz) technology. By biasing the HBT devices around tire peak transit-time frequency (f_T), the operating frequency of a D-FF with ECNFP (emitter-coupled negative feedback pairs) can be improved. At a supply voltage of 5 y a divide-by-two function of 9.5 GHz is achieved.     

Microwave circuit characteristics of bulk GaAs oscillators

The microwave circuit characteristics of bulk GaAs transit-time mode and limited space-charge accumulation (LSA) mode oscillators have been evaluated experimentally and theoretically. Experimental measurements were performed with a waveguide-coaxial microwave circuit having two experimental degrees of freedom in which the circuit radiation impedance at the device contacts was evaluated by a dyadic Green's function method. Experiments conducted in three rectangular waveguide circuits at fixed bias voltage have established that the LSA mode frequency tuning range is determined by the magnitude and variation of the circuit series inductive reactance XLrelative to the device low-field resistance R0. At a bias voltage which is twice threshold the tuning range is given by1/2.4leq X_{L}/R_{0}leq 2.4. No fixed, linear equivalent circuit characterizes the LSA mode. Analysis and experimental results indicate that the device impedance of small-signal transit-time mode oscillators changes from a passive parallel RC impedance well below threshold to an impedance just above threshold which can be approximated by a series RLC circuit. The series L and C decrease linearly with transit-time mode harmonic order number.     

A 9–31-GHz Subharmonic Passive Mixer in 90-nm CMOS Technology

A subharmonic down-conversion passive mixer is designed and fabricated in a 90-nm CMOS technology. It utilizes a single active device and operates in the LO source-pumped mode, i.e., the LO signal is applied to the source and the RF signal to the gate. When driven by an LO signal whose frequency is only half of the fundamental mixer, the mixer exhibits a conversion loss as low as 8–11 dB over a wide RF frequency range of 9–31GHz. This performance is superior to the mixer operating in the gate-pumped mode where the mixer shows a conversion loss of 12–15dB over an RF frequency range of 6.5–20 GHz. Moreover, this mixer can also operate with an LO signal whose frequency is only 1/3 of the fundamental one, and achieves a conversion loss of 12–15dB within an RF frequency range of 12–33 GHz. The IF signal is always extracted from the drain via a low-pass filter which supports an IF frequency range from DC to 2 GHz. These results, for the first time, demonstrate the feasibility of implementation of high-frequency wideband subharmonic passive mixers in a low-cost CMOS technology.     

High-frequency performance of submicrometer channel-length siliconMOSFETs

Polycide-gate silicon n-channel MOSFETs were fabricated on the basis of a standard 0.5-μm MOS technology and measured over the 1.5-26.5-GHz frequency range, in order to investigate the effects of channel-length reduction on device behavior at high frequency. Excellent microwave performances were obtained with a maximum operating frequency (f_max) and a unity-current-gain frequency f _t near 20 GHz for 0.5-μm-gate-length NMOS devices. An equivalent circuit for a MOSFET with its parasitic elements was extracted from measured S-parameter data. The influence of gate resistance, gate-to-drain overlap capacitance, substrate conductivity, and the transit-time effect between the source and drain on microwave characteristics was analyzed     

Second harmonic operation at 460 GHz and broadband continuous frequency tuning of a gyrotron oscillator

We report the short-pulse operation of a 460 GHz gyrotron oscillator both at the fundamental (near 230 GHz) and second harmonic (near 460 GHz) of electron cyclotron resonance. During operation in a microsecond pulse length regime with 13-kV beam voltage and 110-mA beam current, the instrument generates several watts of power in two second harmonic modes, the TE/sub 2,6,1/ at 456.15 GHz and the TE/sub 0,6,1/ at 458.56 GHz. Operation in the fundamental modes, including the TE/sub 0,3,1/ mode at 237.91 GHz and the TE/sub 2,3,1/ at 233.15 GHz, is observed at output powers up to 70 W. Further, we demonstrate broadband continuous frequency tuning of the fundamental modes of the oscillator over a range of more than 2 GHz through variation of the magnetic field alone. We interpret these results in terms of smooth transitions between higher order axial modes of the resonator. The 460 GHz gyrotron is currently being processed for continuous duty operation, where it will serve as a microwave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) studies at 16 T (700 MHz /sup 1/H), a field strength which is two-fold higher than has been accessible with previous technology.     

A 94/47 GHz frequency halver using a GaAs Gunn device

This paper describes the basic principles and the set up of a new kind of frequency halvers suited for millimeter wave applications. A Ga As Gunn-device is used to act like a nonostable multivibrator having a hold time adequate to the domain transit time T_t of the Gunn-device. In a certain frequency range depending on the transit frequency f_T=1/T_T, bias voltage and circuit parameters a harmonic wave synchronized fundamental/2nd harnonic mode oscillator is able to perform as a frequency halver. An input power of only 1mW is sufficient to achieve a bandwidth of 5 GHz respectively 2.5 GHz centered around 94 GHz respectively 47GHz. Since the output power is 50 mW at fundamental frequency f_F, this halver offers 17dB conversion gain.     

A 98/196 GHz Low Phase Noise Voltage Controlled Oscillator With a Mode Selector Using a 90 nm CMOS Process

A 98/196 GHz low phase noise voltage controlled oscillator (VCO) with a fundamental/push-push mode selector using a 90 nm CMOS process is presented in this letter. An innovative concept of the VCO with the mode selector is proposed to switch the fundamental or second harmonic to the RF output. The VCO demonstrates a fundamental frequency of up to 98 GHz with an output power of greater than $-8~{rm dBm}$. The phase noise of the VCO is better than $-100.8~{rm dBc}/{rm Hz}$ at 1 MHz offset frequency, and its figure-of-merit is better than $-186~{rm dBc}/{rm Hz}$. Moreover, the output frequency of the work is up to 196 GHz with a fundamental suppression of greater than $-30~{rm dBc}$ as the VCO is operated in push-push mode.      

Diffusion-barrier contacts based on the TiN and Ti(Zr)Bx interstitial phases in the microwave diodes for the range of 75–350 GHz

A new technology for thermally stable ohmic contacts with diffusion barriers based on the amorphous TiN and Ti(Zr)B_x interstitial phases is used in the development of microwave diodes for the millimeter region (with the frequency higher than 100 GHz) based on GaAs, InP, and Si. It became possible to increase the reliability of the GaAs-and InP-based Gunn diodes that operate at the frequency of 200 GHz by using the epitaxial layers formed on porous III–V substrates by gas-phase, molecular-beam, and liquid-phase epitaxy as the initial device structures. The range of emission from the avalanche transit-time diodes based on Si is extended to 350 GHz. To this end, the technology of forming the active element on the silicon metallized diaphragm is used for the first time.