Schottky Diode Detector Research Articles

Terahertz digital holography using angular spectrum and dual wavelength reconstruction methods

Terahertz digital off-axis holography is demonstrated using a Mach-Zehnder interferometer with a highly coherent, frequency tunable, continuous wave terahertz source emitting around 0.7 THz and a single, spatially-scanned Schottky diode detector. The reconstruction of amplitude and phase objects is performed digitally using the angular spectrum method in conjunction with Fourier space filtering to reduce noise from the twin image and DC term. Phase unwrapping is achieved using the dual wavelength method, which offers an automated approach to overcome the 2π phase ambiguity. Potential applications for nondestructive test and evaluation of visually opaque dielectric and composite objects are discussed.

A 0.25-.MU.m Si-Ge Fully Integrated Pulse Transmitter with On-Chip Loop Antenna Array towards Beam-Formability for Millimeter-Wave Active Imaging

This paper presents a 100-120-GHz pulse transmitter chip with a 54×24 on-chip loop antenna array for the purpose of beam-formability in portable millimeter-wave (mm-wave) active imaging applications. We present a new idea for silicon-based mm-wave pulse beam-forming by using voltage-varied CMOS inverter chain. This 4-mm×4-mm transmitter chip is designed and fabricated in a 2.5-V 0.25-µm 4-metal-layer Si-Ge Bi-CMOS process. The 30-µm × 30-µm loop antenna located on the top-metal layer operates as an coil in an integrated mm-wave pulse generator. Each of on-chip pulse generators employing under-damped/over-damped conditions to produce mm-wave pulses includes an R-L-C circuit, a bipolar junction transistor (BJT) operated as a switch and a CMOS inverter chain circuit for shaping the rising edge of the input clock. Simulation results by ADS 2009 and HSPICE show that loop antenna' inductance and resistance at 80-120-GHz are 51pH and 3Ω, respectively. A simulation performance of an integrated 13×6 loop antenna array illustrates the variation of maximum radiation angles depending on different phase values between array's elements. By using an mm-wave power meter, a 90-140-GHz standard horn antenna and a Schottky diode detector, several measured radiation patterns of this loop antenna array chip are achieved. From the measurement result, we demonstrate the possibility of an integrated mm-wave pulse generator for the purpose of beam-forming by changing power supplies of inverter chains.

Progress and Challenges Towards Terahertz CMOS Integrated Circuits

Key components of systems operating at high millimeter wave and sub-millimeter wave/terahertz frequencies, a 140-GHz fundamental mode voltage controlled oscillator (VCO) in 90-nm CMOS, a 410-GHz push-push VCO with an on-chip patch antenna in 45-nm CMOS, and a 125-GHz Schottky diode frequency doubler, a 50-GHz phase-locked loop with a frequency doubled output at 100 GHz, a 180-GHz Schottky diode detector and a 700-GHz plasma wave detector in 130-nm CMOS are demonstrated. Based on these, and the performance trends of nMOS transistors and Schottky diodes fabricated in CMOS, paths to terahertz CMOS circuits and systems including key challenges that must be addressed are suggested. The terahertz CMOS is a new opportunity for the silicon integrated circuits community.

Application of Zero-Bias Quasi-Optical Schottky-Diode Detectors for Monitoring Short-Pulse and Weak Terahertz Radiation

Schottky diodes are well-known nonlinear elements allowing for effective detection and mixing of electromagnetic radiation in the range through microwave to terahertz. Although less sensitive than their superconducting counterparts, they generally do not require cooling that makes them the devices of choice for applications where the ultimate sensitivity is not needed. In the emerging field of terahertz technology, there is a long-time quest for cheap and handy detectors for laboratory use, as well as for serial compact and midsize instruments. We describe the use of a quasi-optically coupled zero-bias planar Schottky-diode detector for monitoring picosecond pulses of synchrotron terahertz radiation and weak continuous-wave emission from an array of Josephson junctions.

Cyclostationary Shot-Noise Measurements in RF Schottky-Barrier Diode Detectors

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Homodyne (zero-IF) operation is very prone to low-frequency noise, partially contributed by the solid-state detector operated in large-signal (quasi-)periodic conditions. Shot noise is the major contributor to this noise if the detector is operated beyond its noise corner frequency. In this letter, we experimentally observe that the current spectral density of this shot noise in Schottky diode detectors is different from the conventional <formula formulatype="inline"><tex Notation="TeX">$\hbox{2}qI$</tex></formula>, where <formula formulatype="inline"><tex Notation="TeX">$I$</tex> </formula> is the average current. It is found that it varies as <formula formulatype="inline"><tex Notation="TeX">$\hbox{2}nkT/R_{ \rm dp}$</tex></formula>, where <formula formulatype="inline"><tex Notation="TeX">$n$</tex></formula> is the diode ideality factor and <formula formulatype="inline"><tex Notation="TeX">$R_{\rm dp}$</tex></formula> is the small-signal resistance of the pumped diode that can be very different from the standard-diode small-signal resistance obtained from the differential of the <formula formulatype="inline"><tex Notation="TeX">$I$</tex></formula>–<formula formulatype="inline"><tex Notation="TeX">$V$</tex> </formula> characteristic. To the best of our knowledge, this behavior was anticipated theoretically a long time ago but has been seldom addressed experimentally. </para>

LFI 30 and 44 GHz receivers Back-End Modules

The 30 and 44 GHz Back End Modules (BEM) for the Planck LowFrequency Instrument are broadband receivers (20% relative bandwidth)working at room temperature. The signals coming from the Front EndModule are amplified, band pass filtered and finally converted to DCby a detector diode. Each receiver has two identical branchesfollowing the differential scheme of the Planck radiometers. The BEMdesign is based on MMIC Low Noise Amplifiers using GaAs P-HEMTdevices, microstrip filters and Schottky diode detectors. Theirmanufacturing development has included elegant breadboard prototypesand finally qualification and flight model units. Electrical,mechanical and environmental tests were carried out for thecharacterization and verification of the manufactured BEMs. Adescription of the 30 and 44 GHz Back End Modules of Planck-LFIradiometers is given, with details of the tests done to determinetheir electrical and environmental performances. The electricalperformances of the 30 and 44 GHz Back End Modules: frequencyresponse, effective bandwidth, equivalent noise temperature, 1/f noiseand linearity are presented.

Development of Integrated Terahertz Broadband Detectors Utilizing Superconducting Hot-Electron Bolometers

We report on the development of terahertz broadband detectors utilizing superconducting hot-electron bolometers and planar sinuous antennas. In this work, sinuous antennas designed to cover the frequency range of 50 GHz to nearly 900 GHz have been fabricated on semi-insulating silicon substrates. To maintain a self-complementary structure, four antenna arms are used, leading to a frequency-independent input impedance of 74 Omega. Two squares of superconducting niobium HEBs are required at the feed point of the antennas as the sheet resistance of a 10 nm thick niobium thin film is 35 Omega/square. Two sizes of HEBs (120 nm times 240 nm, and 2 mum times 4 mum) have been fabricated using e-beam lithography (EBL), and standard photolithography processes, respectively. A quasi-optical mount with high-resistivity silicon lens has been employed for coupling input power to the sinuous antenna. With a close-cycled cryocooler, the detector performance is studied and evaluated. Detector responsivity at 585 GHz has been presented and compared to waveguide Schottky diode detectors. Noise equivalent power (NEP) measurement is discussed and will be soon performed to the detectors developed in this paper.

Analysis of Pulsed THz Imaging Using Optical Character Recognition

Using a reflection-based pulsed THz imaging system built upon our ErAs:GaAs photoconductive switch and a gated receiver, we quantify image quality at different detection bands (centered at 100, 400, and 600 GHz). Zero-bias Schottky diode detectors mounted in various waveguide sizes are used to tune the operational frequency bands of the imaging system, while the rest of the imaging system remains unchanged. The image quality is quantified by applying an optical character recognition (OCR) algorithm on THz images of 8-by-10 mm copper letters on a fiberglass substrate. Using the OCR success rate as a metric, we see a fivefold improvement in image quality from a 400 GHz to a 600 GHz imaging system, while our 100 GHz images do not produce any correct OCR results. In a comparison experiment performed at 600 GHz, the image signal-to-noise ratio (SNR) is degraded by placing increasing numbers of denim sheets (5.4 dB decrease in signal per layer) into the beam path. We find that the OCR success rate is roughly constant from one sheet to four sheets of denim (33-25 dB SNR) and then drops off sharply starting at five denim sheets.

Design and Analysis of a Multiport Circuit for Shaping Sub-Nanosecond Pulses

In this study, a coupled-line coupler was evaluated for its potential to shape sub-nanosecond ultra-wideband (UWB) pulses. The coupler was shown to exhibit a natural tendency to differentiate sub-nanosecond pulses, owing to its bandpass nature. Next, a Schottky detector diode was applied to confirm that the small parasitic reactance in the coupler gives rise to the differentiation behavior. The unconventional application of a coupler and Schottky diode towards signal differentiation culminated in the development of a novel UWB generator that simultaneously produces: a square waveform that has a 20%-80% rise time of 850 ps, a Gaussian waveform that has a pulse duration of 100 ps, and a monocycle waveform that has a 80 ps rise time between its peaks. These waveforms were obtained by taking advantage of the dc isolation of the coupled line structure and using step recovery diodes to compress the edges of a 14 MHz sinusoidal source. The resulting multiport circuit for simultaneous shaping of sub-nanosecond pulses (MCS3P) showed good agreement between measured and simulated results.

Generation and Modulation of a 94-GHz Signal Using Electrooptic Modulators

Wireless data transmission at 10.6 Gb/s on a 94-GHz carrier is achieved using photonic components operating at frequencies less than 18 GHz, including a laser diode, two lithium niobate modulators, and an arrayed waveguide grating. A uni- traveling-carrier photodiode is used to convert the doubly modulated optical signal to a modulated millimeter-wave (mmW) carrier. Two antennas are used to transmit and receive the data-encoded mmW signal. A Schottky-diode detector is used to detect the on-off keyed data on the mmW signal at power levels greater than –20 dBm. MMW wireless signals are measured out to a distance of 800 m.

A new multichannel interferometer system on HL-2A

A new multichannel HCN interferometer has been developed on HL-2A tokamak, which is characterized by two techniques: (1) the wave-guide HCN laser with cavity length of 6 m to increase the optical resource power and (2) high response room temperature waveguide Schottky diode detectors to obtain good beat signal. The space resolution is 7 cm by the use of focusing metal mirrors mounted on the vacuum chamber and a compensated optical system. In the 2006 experiment campaign, this new interferometer has been applied for plasma density profile and density sawtooth measurement.

Design and development of batch fabricatable metal–insulator–metal diode and microstrip slot antenna as rectenna elements

Thin-film Ni-NiO-Cr metal–insulator–metal (MIM) tunnel diodes with 1 μm 2 contact area and 1–3 nm insulator layer (NiO) are fabricated for high sensitive far-infrared (IR) detection. Also, a 2.5 GHz microstrip slot antenna is fabricated on a FR-4 substrate and integrated with a commercially available surface mount zero bias Schotky diode. Asymmetric current–voltage ( I–V) characteristics of the MIM tunnel diode is observed with a significant degree of non-linearity. Additionally, the sensitivity of the MIM diode is determined to be 5 V −1 at V bias of 0.1 V. For the antenna coupled detector circuit, the radiation patterns, scattering parameters, output voltage and sensitivity are determined experimentally. Further, when the slot antenna is coupled with the schottky diode detector, a rectified output voltage of 56 mV is obtained by radiating the device with a low frequency tube antenna.

A simple far-infrared laser interferometer for measuring electron densities in reactive low-temperature plasmas

A sensitive far-infrared (fir) interferometer for electron density measurements in reactive low-temperature plasmas is described. The instrument is based on an optically pumped fir laser (wavelength range 50–600μm depending on the working gas) and makes use of the nonlinear relation between output power and cavity loss. The fir beam, which leaves the resonator through a coupling hole in the end mirror, is reflected back into the cavity, such that the coupling hole behaves like a variable “leak” with a loss rate depending on the phase of the reentering wave relative to the standing wave within the resonator. As a result of the feedback, the output intensity undergoes strong nonlinear variations if the optical distance of the external mirror is changed by small amounts, Δz. The power variation is monitored through a small opening in the external mirror. Test experiments using a wavelength of 432.6μm and a Schottky-diode detector have yielded a minimum detectable pathlength variation of Δz=0.4μm, corresponding to a change of the line-integrated electron density n¯e×L of about 5×1015m−2. A first application to argon plasmas in inductively coupled rf discharges has been made, and the results have been compared to concomitant Langmuir probe measurements.

Near room temperature X-ray and [formula omitted]-ray spectroscopic detectors for future space experiments

New generation Cadmium Telluride (CZT and CdTe) solid-state detectors can provide high quantum efficiency with reasonably good energy resolution and can operate at near room temperature; a unique advantage for space experiments. We present here results of our study of small diode detectors as well as large area pixel detectors. Our study is aimed at developing near room temperature hard X-ray spectroscopy detectors for ASTROSAT and other future Indian space science missions. We have studied a Si-PIN detector in the energy range 5–60 keV and CZT and CdTe Schottky diode detectors in the energy region 10–1330 keV. Our results suggest that the energy resolution is limited by the thermal/electronic noise in the low-energy region ( ⩽ 60 keV ) while it is affected by the charge transport properties of the detector in the higher energy region ( ⩾ 100 keV ) . We have studied large area ( 64 cm 2 ) CZT pixel detectors with pixel size close to the small CZT detector. We have studied individual pixels as well as CZT detector as a whole (summed over all the 1024 pixels). The CZT pixel detectors are single carrier detectors with peaking time ⩽ 1 μ s . The energy resolution behaviour of the large area CZT detector is similar to that of small diode detectors in the low-energy region. The change in operating temperature from room temperature ∼ 20 to ∼ 70 ∘ C drastically affects both the energy resolution as well as the peak area due to a sharp rise in the thermal noise. These results suggest that the cooling of detector system will provide better energy resolution as well as detection efficiency. Our results also show that the crystal uniformity is another important issue in the case of large area CZT pixel detectors.

Compact continuous-wave subterahertz system for inspection applications

We report the use of a compact continuous-wave sub-terahertz system for inspection applications, using electronic generation and detection methods. A combination of a Gunn diode emitter, a Schottky diode detector, and a polyethylene Fresnel lens provides line-scan images at 0.2m∕s with a data acquisition rate of 512points∕s. Examples of the measurement of NASA’s insulating panels and applicability of the technology to other nondestructive testing applications are presented and discussed.

Special Features of Charge Transport in Schottky Diodes Based on Semi-insulating CdTe

The electrical characteristics of CdTe-based Schottky-diode detectors of X-ray and γ radiation are studied. Experimental data are obtained for Al/p-CdTe diodes with a substrate resistivity from 102 to 109 Ωcm (300 K). The obtained results are interpreted in the context of the Sah-Noyce-Shockley theory of generation-recombination, taking into account the special features of the Schottky diode. It is shown that, when semi-insulating CdTe is used, the considerable forward currents observed are caused by electron injection into the substrate.

Sensitivity of high temperature superconducting Josephson detectors at millimetre-wave band

Sensitivity of high temperature superconducting (HTS) Josephson detectors at millimetre-wave band has been studied in detail. YBCO grain boundary Josephson junctions with the normal-state resistance (RN) around 1 Ω and ICRN product of less than 2 mV have been fabricated for this study, where IC is the critical current of the junction. A Gunn oscillator at the frequency of 98 GHz together with a set of calibrated attenuators with a total attenuation of 90 dB are used as a signal source. A quasi-optical system, which consists of a wideband planar log-periodic antenna encompassing the junction, parabolic mirrors and a hyperhemispherical silicon lens, has been used as an effective coupling system. Sensitivity increases with ICRN. Using a junction with ICRN of 300 µV, a sensitivity of about 9000 V W−1 has been obtained, which is higher than that of the Schottky diode detectors at the same frequency band and demonstrates that the HTS Josephson detectors are very sensitive at millimetre-wave band.

Design and testing of ECE radiometer for Sinp-Tokamak

A multi channel ECE Radiometer, in the frequency range of 75 - 110 GHz, has been designed, constructed and tested for the SINP-Tokamak to diagnose second harmonic X-mode electron cyclotron emission (ECE). This frequency range covers approximately 80% of the plasma cross section in case of a magnetic eld of B = 1.5 T. For the maximum field of the SINP-Tokamak B = 2.0 T, about 50% is covered. The ECE radiation is received by a single horn antenna with a gain of approximately 30 dB. To increase the spatial resolution perpendicular to the line of sight, a focusing lens is employed. The incoming radiation power is split into two branches by a 3dB coupler. Before down conversion of the input spectrum, the upper and the lower side band are selected respectively by means of a high pass and a low pass filter. Behind the filters, identical components are employed. The local oscillator frequency is 92 GHz for both mixers. The IF frequency range after down conversion is 2 to 18 GHz. The IF spectrum is amplified by two amplifiers with a total gain of approximately 60 dB. The outputs of these amplifiers are split into 6 branches. The frequency selection is made by band pass filters and the received power is detected by Schottky diode detectors followed by video amplification and ltering. The data is recorded by an ADC with 1 MHz sampling rate. The radiometer has been tested and calibrated with a high temperature blackbody radiator. The effective input noise temperature for the radiometer channels is found to be in the order of 0.1 eV. The linear regime of operation extends up to an input power which corresponds to an electron temperature of approximately 200 eV. Above this temperature the 1 dB compression point of the Schottky diode detectors is exceeded and the IF gain should be reduced. This can be easily done by incorporating appropriate attenuator behind the IF amplifiers.

Frequency-domain EBIC method for mapping of noise and instability regions in semiconductor devices

A frequency-domain electron beam induced current (EBIC) method for visualisation and analysis of noise-enhancement and/or instability regions related to generation–recombination effects in semiconductor devices is presented. The method is illustrated with examples. EBIC map of the InGaAsP/InP avalanche photodiode at the avalanche breakdown is compared with the EBIC map of current noise at the avalanche breakdown. Instability domains in Au/SI GaAs Schottky diode detector structures are visualised for the first time to our best knowledge.

Radiation hardness of SiC based ions detectors for influence of the relative protons

Nuclear detector radiation hardness is very important for key experiments in high-energy physics, where the irradiation fluence of relativistic particles can be as high as 10 15 cm −2. In this work, we investigate the radiation hardness of SiC Schottky diode detectors φ600 μm, obtained by magnetron sputtering of Ni on surface of 6H–SiC films, grown by sublimation epitaxy in vacuum. Irradiation has been performed using 1 GeV protons. Detector characteristics were tested by α-particles from a 244Cm source (5.79 MeV). Investigation of the detector parameters (diffusion length, radiation-induced defects concentration, thickness of the space charge region), before and after irradiation shows that, up to a fluence of 3×10 14 cm −2 , the device degradation is at a beginning stage.