We present InP-based Triple Barrier Resonant Tunneling Diodes monolithically integrated with an on-wafer resonant or broad band antenna. Biasing these diodes in the negative differential resistance regime provides a fundamental mode oscillation of preliminary 90 μW at f0 = 260 GHz. At 280 GHz an estimated high zero-bias resonant responsivity of 50.000 V/W is modeled. A broad band average responsivity of 900 V·W-1 was determined in the frequency range from 230 … 330 GHz along with a minimum Noise Equivalent Power of 1 pW·Hz-0.5. This concept is expected to provide very high sensitivities at frequencies up to f ≥ 1 THz.
Several terahertz-wave radar techniques based on a resonant-tunneling-diode (RTD) oscillator are under investigation. First, an amplitude-modulated continuous-wave (AMCW) radar able to measure the absolute distance was achieved by demodulating the wave returning from the target and measuring its phase, either by determining the time delay with an oscilloscope, or by using an IQ demodulator to determine the sine and cosine of the phase. Our current record with this type of radar is a ranging error of 0.063 mm; however, it can only measure the distance up to a single reflecting surface. Second, a subcarrier frequency-modulated continuous-wave (FMCW) radar has been demonstrated to work and is expected to allow the simultaneous ranging of several targets. The ranging error for this radar was found to be 0.73 mm. Additionally, a radar technique based on the swept source optical coherence tomography (SS-OCT) principle is proposed. Terahertz-wave 2D imaging can be combined with these radar techniques to obtain a 3D imaging system.
Compact and coherent source is a key component for various applications of the terahertz wave. We report on our recent results of terahertz oscillators using resonant tunneling diodes (RTDs). The RTD is an InGaAs/AlAs double-barrier structure on InP substrate, and integrated with a planar slot antenna as a resonator and radiator. The output power is obtained from the substrate side through a Si lens. To achieve high-frequency oscillation, a narrow quantum well and an optimized collector spacer thickness were used. The former reduces the electron dwell time in the resonant tunneling region and the latter simultaneously reduces the electron transit time and the capacitance at the collector depletion region. The conduction loss of the slot antenna was also reduced with an optimized antenna length and an improved air bridge structure between the RTD and antenna. By these structures, fundamental oscillation up to 1.92 THz were obtained at room temperature. Oscillation above 2 THz is further expected in theoretical calculation. An oscillator with patch antenna, in which a Si lens is unnecessary, was fabricated. In a preliminary experiment, output power of 55 μW was obtained at 1 THz in a three-element array. Wireless data transmission using direct intensity modulation was demonstrated with the data rate of 30 Gbp/s and the bit error rate below the forward error correction limit. By integrating a varactor into the slot antenna, electrical frequency tuning was achieved with a tuning range of 580-900 GHz in an array device. Application of frequency-tunable RTD oscillators to measurements of absorption spectra was also demonstrated.
Recent progress in room-temperature resonant-tunneling-diode (RTD) terahertz (THz) oscillators and high-electron-mobility- transistor (HEMT) THz receivers is reported in this paper. In this study, oscillations up to 1.86 THz were obtained using an optimized antenna and RTD. Using a two-element oscillator array, high output power of 0.6 mW at 620 GHz was obtained. THz communication up to 3 Gbps was demonstrated. A structure for high-speed direct modulation was fabricated, and the intensity modulation up to 30 GHz was achieved. A novel oscillator structure was proposed and fabricated for extraction of output power without using a Si lens. A short-gate InGaAs HEMT detector integrated with a broadband bow-tie antenna was fabricated, and a high current sensitivity of ~5 A/W was obtained at 280 GHz.
Our recent results of room-temperature THz oscillators using resonant tunneling diodes (RTDs) are reported. This
oscillator is composed of a GaInAs/AlAs double-barrier RTD and a planar slot antenna. The maximum oscillation
frequency in RTDs is limited by the electron delay time across the RTD layers, which consists of the dwell time in the
resonant tunneling region and the transit time across the collector depletion region. The dwell time was reduced by a
narrow quantum well, and a fundamental oscillation up to 1.31 THz with the output power of 10 μW was achieved at
room temperature. Further increase in oscillation frequency is expected by optimized size and materials of the well and
barriers for the dwell time and those of the collector depletion layer for the transit time. By these improvements, a
fundamental oscillation up to around 2 THz is theoretically possible. For high output power, coherent power combining
was demonstrated in a two-element array with offset slot antennas coupled with each other, and 610 μW at 620 GHz was
obtained. Spectral characteristics were measured with a heterodyne detection, and the linewidth of less than 10 MHz was
obtained. A frequency change of 1-5 % with bias voltage was also observed, which is attributed to the bias-dependent
dwell time. Direct intensity modulation and wireless data transmission were demonstrated. A transmission rate of 3 Gbps
with the bit error rate of 3×10-5 was obtained at 540 GHz in a preliminary experiment, which is limited by the frequency
characteristics of external modulation circuits at present.
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