Optical Noise Equivalent Power Research Articles

A Graphene-Based Terahertz Hot Electron Bolometer with Johnson Noise Readout

In this paper, we present the development of a graphene-based hot electron bolometer with Johnson noise readout. The bolometer is a graphene microbridge connected to a log spiral antenna by Au contact pads. The Fourier transform spectrometer measurement shows the bolometer has high coupling efficiency in the frequency range from 0.3 to 1.6 THz. Using 300/77 K blackbody loads, we measure an optical noise equivalent power of 5.6 × 10−12 W/Hz0.5 at 3.0 K. To understand the thermal transport inside the graphene microbridge, we measure the bolometers with different microbridge lengths at different bath temperatures. We find that the thermal conductance due to electron diffusion is significant in the bolometers.

Twin-Slot Antenna-Coupled Superconducting Ti Transition-Edge Sensor at 350 GHz

We have developed four-leg-supported superconducting Ti transition-edge sensors (TES) formed by KOH wet etching. Energy relaxation mechanism is changed from electron–phonon coupling to diffusive phonon after wet etching. The current–voltage curves of the same TES device were measured before and after wet etching. After wet etching, its thermal conductance (G) is reduced to 500 pW/K from 8950 pW/K. The measured effective response time (τeff) is 143 μs, about 30 times larger. In addition, we have studied the optical noise equivalent power (NEP) with a cryogenic blackbody in combination with metal-mesh filters to define the radiation bandwidth. The obtained optical NEP is 5 × 10−16 W/√Hz, which is suitable for ground-based astronomical applications.

Nonlinear Analysis of Nonresonant THz Response of MOSFET and Implementation of a High-Responsivity Cross-Coupled THz Detector

The nonresonant THz response of CMOS FET has been analyzed based on static nonlinearities of the transistor channel. For the applied gate-to-source and drain-to-source signals, the significance of the second-order nonlinear terms is investigated as a function of dc bias conditions. A cross-coupled design for differential excitation of the THz detector is also proposed, and it has been shown, based on analysis as well as through measurements, that a cross-coupled detector topology can give the highest responsivity in an unbiased-drain operation, among the possible detector topologies. A minimum optical noise equivalent power (NEP) of $\text{29 pW}/\surd \text{Hz}$ is measured for the cross-coupled detector topology at 500 GHz with unbiased drain. The change in the polarity of the detector response under certain bias conditions is also explained. This paper gives a comprehensive picture of the behavior of the CMOS THz detector by discussing the design considerations such as readout modes, optimum bias points, and device dimensions with respect to both responsivity and NEP.

Attojoule energy resolution of direct detector based on hot electron bolometer

We characterize superconducting antenna-coupled NbN hot-electron bolometer (HEB) for direct detection of THz radiation operating at a temperature of 9.0 K. At signal frequency of 2.5 THz, the measured value of the optical noise equivalent power is 2.0×10-13 W-Hz-0.5. The estimated value of the energy resolution is about 1.5 aJ. This value was confirmed in the experiment with pulsed 1.55-μm laser employed as a radiation source. The directly measured detector energy resolution is 2 aJ. The obtained risetime of pulses from the detector is 130 ps. This value was determined by the properties of the RF line. These characteristics make our detector a device-of-choice for a number of practical applications associated with detection of short THz pulses.

THz Detection Using p+/n-Well Diodes Fabricated in 45-nm CMOS

Electronic-detection up to $\sim 0.9$ THz using p+/n-well junction diodes in a 45-nm bulk CMOS process is demonstrated. Because the 1/f noise corner frequency is $\sim 1$ kHz instead of $\sim 10$ MHz common to Schottky and diode-connected nMOS transistor detectors, despite lower responsivity, detectors using a p+/n-well diode with an optimized transit time achieve competitive noise equivalent power (NEP) while exhibiting smaller variations. The junction diode has a measured zero-bias cutoff frequency ( $f_{T}$ ) of $\sim 1.8$ THz. The direct-antenna matched structure can reach a peak optical responsivity ( $R_{v}$ ) of 558 V/W at 0.781 THz with a minimum optical NEP of 56 pW/Hz0.5 at a modulation frequency of 100 kHz.

THz Direct Detector and Heterodyne Receiver Arrays in Silicon Nanoscale Technologies

The main scope of this paper is to address various implementation aspects of THz detector arrays in the nanoscale silicon technologies operating at room temperatures. This includes the operation of single detectors, detectors operated in parallel (arrays), and arrays of detectors operated in a video-camera mode with an internal reset to support continuous-wave illumination without the need to synchronize the source with the camera (no lock-in receiver required). A systematic overview of the main advantages and limitations in using silicon technologies for THz applications is given. The on-chip antenna design challenges and co-design aspects with the active circuitry are thoroughly analyzed for broadband detector/receiver operation. A summary of the state-of-the-art arrays of broadband THz direct detectors based on two different operation principles is presented. The first is based on the non-quasistatic resistive mixing process in a MOSFET channel, whereas the other relies on the THz signal rectification by nonlinearity of the base-emitter junction in a high-speed SiGe heterojunction bipolar transistor (HBT). For the MOSFET detector arrays implemented in a 65 nm bulk CMOS technology, a state-of-the-art optical noise equivalent power (NEP) of 14 pW/ $\sqrt {Hz}$ at 720 GHz was measured, whereas for the HBT detector arrays in a 0.25 μm SiGe process technology, an optical NEP of 47 pW/ $\sqrt {Hz}$ at 700 GHz was found. Based on the implemented 1k-pixel CMOS camera with an average power consumption of 2.5 μW/pixel, various design aspects specific to video-mode operation are outlined and co-integration issues with the readout circuitry are analyzed. Furthermore, a single-chip 2 × 2 array of heterodyne receivers for multi-color active imaging in a 160–1000 GHz band is presented with a well-balanced NEP across the operation bandwidth ranging from 0.1 to 0.24 fW/Hz (44.1–47.8 dB single-sideband NF) and an instantaneous IF bandwidth of 10 GHz. In its present implementation, the receiver RF bandwidth is not continuously covered but divided into six bands centered around 165, 330, 495, 660, 820, and 990 GHz.

A Microwave Reflection Readout Scheme for Hot Electron Bolometric Direct Detector

In this paper, we propose and present data from a fast THz detector based on the repurpose of hot electron bolometer mixers (HEB) fabricated from superconducting NbN thin film. This detector is essentially a traditional NbN bolometer element that operates under the influence of a microwave pump. The injected microwave power serves the dual purpose of enhancing the detector sensitivity and reading out the impedance changes of the device in response to incident THz radiation. We have measured an optical Noise Equivalent Power of 4 pW/ ${\surd{\hbox{Hz}}}$ for our detector at a bath temperature of 4.2 K. The measurement frequency was 0.83 THz and the modulation frequency was 1.48 kHz. The readout scheme is versatile and facilitates both high-speed operation as well as multi-pixel applications.

Equivalence of optical and electrical noise equivalent power of hybrid NbTiN-Al microwave kinetic inductance detectors

We have measured and compared the response of hybrid NbTiN-Al Microwave Kinetic Inductance Detectors (MKIDs) to changes in bath temperature and illumination by sub-mm radiation. We show that these two stimulants have an equivalent effect on the resonance feature of hybrid MKIDs. We determine an electrical noise equivalent power (NEP) from the measured temperature responsivity, quasiparticle recombination time, superconducting transition temperature, and noise spectrum, all of which can be measured in a dark environment. For the two hybrid NbTiN-Al MKIDs studied in detail, the electrical NEP is within a factor of two of the optical NEP, which is measured directly using a blackbody source.

Antenna-integrated 0.6 THz FET direct detectors based on CVD graphene.

We present terahertz (THz) detectors based on top-gated graphene field effect transistors (GFETs) with integrated split bow-tie antennas. The GFETs were fabricated using graphene grown by chemical vapor deposition (CVD). The THz detectors are capable of room-temperature rectification of a 0.6 THz signal and achieve a maximum optical responsivity better than 14 V/W and minimum optical noise-equivalent power (NEP) of 515 pW/Hz(0.5). Our results are a significant improvement over previous work on graphene direct detectors and are comparable to other established direct detector technologies. This is the first time room-temperature direct detection has been demonstrated using CVD graphene, which introduces the potential for scalable, wafer-level production of graphene detectors.

Fast and Sensitive Terahertz Direct Detector Based on Superconducting Antenna-Coupled Hot Electron Bolometer

We characterize superconducting antenna-coupled hot-electron bolometers for direct detection of terahertz radiation operating at a temperature of 9.0 K. The estimated value of responsivity obtained from lumped-element theory is strongly different from the measured one. A numerical calculation of the detector responsivity is developed, using the Euler method, applied to the system of heat balance equations written in recurrent form. This distributed element model takes into account the effect of nonuniform heating of the detector along its length and provides results that are in better agreement with the experiment. At a signal frequency of 2.5 THz, the measured value of the optical detector noise equivalent power is $2.0 \times 10^{-13} \hbox{W}\cdot\hbox{Hz}^{-0.5}$ . The value of the bolometer time constant is 35 ps. The corresponding energy resolution is about 3 aJ. This detector has a sensitivity similar to that of the state-of-the-art sub-millimeter detectors operating at accessible cryogenic temperatures, but with a response time several orders of magnitude shorter.

A Microwave-Operated Hot-Electron-Bolometric Power Detector for Terahertz Radiation

A new class of microwave-operated THz power detectors based on the NbN hot-electron-bolometer (HEB) mixer is proposed. The injected microwave signal (∼1 GHz) serves the dual purpose of pumping the HEB element and enabling the read-out of the internal state of the device. A cryogenic amplifier amplifies the reflected microwave signal from the device and a homodyne scheme recovers the effects of the incident THz radiation. Two modes of operation have been identified, depending on the level of incident radiation. For weak signals, we use a chopper to chop the incident radiation against a black body reference and a lock-in amplifier to perform synchronous detection of the homodyne readout. The voltage measured is proportional to the incident power, and we estimate an optical noise equivalent power of ∼5pW/ $\surd$ Hz at 0.83 THz. At higher signal levels, the homodyne circuit recovers the stream of steady relaxation oscillation pulses from the HEB device. The frequency of these pulses is in the MHz frequency range and bears a linear relationship with the incident THz radiation over an input power range of ∼15 dB. A digital frequency counter is used to measure THz power. The applicable power range is between 1 nW and 1 $\mu\mathrm{W}$ .

Highly sensitive hot electron bolometer based on disordered graphene.

A bolometer is a device that makes an electrical resistive response to the electromagnetic radiation resulted from a raise of temperature due to heating. The combination of the extremely weak electron-phonon interactions along with its small electron heat capacity makes graphene an ideal material for applications in ultra-fast and sensitive hot electron bolometer. However, a major issue is that the resistance of pristine graphene weakly depends on the electronic temperature. We propose using disordered graphene to obtain a strongly temperature dependent resistance. The measured electrical responsivity of the disordered graphene bolometer reaches 6 × 106 V/W at 1.5 K, corresponding to an optical responsivity of 1.6 × 105 V/W. The deduced electrical noise equivalent power is 1.2 , corresponding to the optical noise equivalent power of 44 . The minimal device structure and no requirement for high mobility graphene make a step forward towards the applications of graphene hot electron bolometers.

CMOS Integrated Antenna-Coupled Field-Effect Transistors for the Detection of Radiation From 0.2 to 4.3 THz

This paper reports on field-effect-transistor-based terahertz detectors for the operation at discrete frequencies spanning from 0.2 to 4.3 THz. They are implemented using a 150-nm CMOS process technology, employ self-mixing in the n-channels of the transistors and operate well above the transistors' cutoff frequency. The theoretical description of device operation by Dyakonov and Shur is extended in order to describe the device impedance, responsivity, and noise-equivalent power for a novel detection concept, which couples the signal to the drain. This approach enables quasi-static (QS) detection and calibration of the detectors. The different transport regimes (i.e., QS, distributed resistive, and plasmonic mixing) and their transitions are theoretically discussed and experimentally accessed. Responsivity values of 350 V/W at 595 GHz, 30 V/W at 2.9 THz, and 5 V/W at 4.1 THz are reported. At 0.595 THz, we determine the optical noise equivalent power (NEP) to be 42 pW/√Hz ; at 2.9 THz, the value is 487 pW/√Hz. All values are reported for optimum gate bias with respect to NEP at 295 K. For 0.595 THz, theory predicts a NEP value at threshold as low as 2 pW/√Hz for ideal coupling of the radiation.

Terahertz Direct Detection in ${\hbox{YBa}}_{2}{\hbox{Cu}}_{3}{\hbox{O}}_{7}$ Microbolometers

A high sensitivity broadband terahertz direct detector based on YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> high-Tc superconductor microbolometers is presented. At 77 K, the responsivity of the spiral antenna-integrated microbolometers (1.5 μm ×1.5 μm) is 190 V/W, referenced to the input of the silicon substrate lens, across the frequency range of 330 GHz-1.63 THz in a single device. The response time is approximately 300 ps. Using a room temperature readout, we measure an optical noise equivalent power (NEP) of 20 pW/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sup> (readout noise limited) for modulation frequencies ranging from 500 Hz to 100 kHz.

Optical characterization of the quantum capacitance detector at 200 μm

We present the optical characterization at 200 μm wavelength of an antenna coupled quantum capacitance detector (QCD), a cryogenic detector based on a single Cooper pair box (SCB). The response of the device to a cryogenic blackbody source and the device noise have been measured giving an optical noise-equivalent power (NEP) at a readout frequency of 10 kHz of 2 × 10−17 W/Hz1/2 at an optical loading of 17 fW. For optical loadings of a few pW, the optical NEP was on the order of 10−16 W/Hz1/2, demonstrating that QCDs could already work as detectors for far-infrared and submillimeter wave radiation in a ground based telescope.

Ultrasensitive TES Bolometers for Space-Based FIR Astronomy

Results of study optical performance of single pixel transition edge sensor (TES) bolometer presented at wavelength band 30-60 μm are presented. FIR radiation is coupled into a multimode horn with entrance aperture of 450 μm, length 4.5 mm and exit aperture of 45 μm , which feeds a metal integrating cavity containing the detector. The radiation band is defined by a pair of lowpass and highpass mesh filters in front of the horn. Here we present measurements of optical noise equivalent power (NEP), optical efficiency, dynamic range and time constant. The results show that measured TES detectors are close to meeting the requirement of the “Band S” of SAFARI FTS imaging instrument on the SPICA mission.

Development of Kinetic Inductance Detectors for Cosmic Microwave Background experiments

We describe the design, optimization, electrical and optical tests of Microwave Kinetic Inductance Detectors (MKIDs) for the mm-wave range. Our detectors are based on a novel resonator design, and are suitable for ground-based astronomical observations in the 143 GHz atmospheric window. The measured optical Noise Equivalent Power (NEP) at 0.3 K is \(\sim 10^{-16}~\text{W}/\sqrt{\rm Hz}\) under a 300 K background load. This is equivalent or better than the performance of the best current bolometric detectors for the 140 GHz atmospheric window, limited by atmospheric noise in the best available sites. We also describe which improvements can be introduced to reduce the NEP of our detector, for lower background applications (narrow band or space-based).

Terahertz spectrum analyzer based on frequency and power measurement

We demonstrate a terahertz (THz) spectrum analyzer based on frequency and power measurement. A power spectrum of a continuous THz wave is measured through optical heterodyne detection using an electromagnetic THz frequency comb and a bolometer and power measurement using a bolometer with a calibrated responsivity. The THz spectrum analyzer has a frequency precision of 1x10(-11), a frequency resolution of 1Hz, a frequency band up to 1.7THz, and an optical noise equivalent power of approximately 1 pW/Hz(1/2).

TES – Technology and Physics

This paper gives an overview of the potential of and developments on Transition Edge Sensors for astronomical research from Space. This type of sensor is under development for imaging X-ray spectrometers as well as for very sensitive InfraRed and sub-mm imaging detectors. This paper describes developments in Europe for the International X-ray Observatory IXO (ESA, JAXA, NASA) and for the SAFARI instrument on the Japanese IR-mission SPICA. The micro-calorimeter array for the IXO-mission will have an imaging array of at least 1024 pixels with high quantum efficiency in the 0.1–10 keV energy range and an energy resolution as small as 2 eV for each detected photon. The SAFARI instrument requires three imaging arrays with an optical Noise Equivalent Power (NEP) as low as ≤ 5 × 10-19 W/√Hz with a total amount of 5940 pixels to read a Fourier Transform Spectrometer. The paper is written to be read together with the presentation given at the Astrophysics Detector Workshop 2008, Nice 17–20 November 2008, France.

MILLIMETER AND SUB-MILLIMETER WAVE PERFORMANCE OF AN ERAS:INALGAAS SCHOTTKY DIODE COUPLED TO A SINGLE-TURN SQUARE SPIRAL

We report the first experimental results for noise-equivalent power (NEP) and noise-equivalent temperature difference (NETD) of single-crystal ErAs:InAlGaAs , zero-bias rectifier diodes coupled to free space quasi-optically in the THz region. At a frequency of 639 GHz, an optical NEP of 4.0×10−12 W / Hz 1/2 is measured with the rectifier coupled to a quasi-plane-wave coherent source through a single-turn square spiral antenna. With a broadband thermal (hot water) source, an NETD of 120 mK is measured from the same device. Antenna radiation patterns at 100 GHz and 639 GHz are also presented.