Balancing the beam: Thermomechanical micromachine detects terahertz radiation

https://www.eurekalert.org/pub_releases/2019-05/iois-btb051519.php

Tokyo, Japan - Radiation from many parts of the electromagnetic spectrum has been harnessed for extremely beneficial uses, in fields as diverse as medicine, imaging and photography, and astronomy. However, the terahertz (THz) region of the spectrum, situated between microwaves and infrared light, has been relatively underutilized owing to difficulties in generating such radiation artificially and in building devices to detect it.

In a breakthrough in the field of terahertz detection, researchers at The University of Tokyo and colleagues have created a thermomechanical device that can sense radiation in the terahertz region of the spectrum in a sensitive and rapid manner, without the need for intense cooling to cryogenic temperatures such as ?270ºC. This device potentially opens up a range of new applications for THz technologies, such as THz cameras.

In this study, reported in the Journal of Applied Physics, the team made use of the heat generated by THz radiation in order to detect it. Specifically, they created a device featuring a tiny beam suspended across a gap, which they then coated with a resistive metal film [nickel-chromium (NiCr) in this case]. This metal film has the ability to absorb THz radiation, which in turn transfers heat to the beam as a whole. This increase in temperature causes the beam to expand very slightly, which can be detected as a change in the frequency at which the beam resonantly vibrates.

"Using our doubly clamped microelectromechanical beam made of gallium arsenide, we could effectively sense THz radiation at room temperature," corresponding author Kazuhiko Hirakawa says. "This structure is particularly effective as it can detect THz radiation very quickly, typically 100 times faster than other conventional room-temperature thermal THz sensors."

This new approach has a range of advantages over existing alternatives for the detection of THz radiation. The fact that it can function at room temperature without the need for cooling makes it suitable for a range of real-world applications. It is also extremely sensitive, detecting radiation that causes changes in temperature as small as one-millionth of a degree.

"Another advantage of this system is that it can be produced using standard methods for fabricating semiconductor devices, which would potentially allow its incorporation into mass-produced THz-based sensors and cameras," according to lead author Ya Zhang. "We hope that our work will lead to an explosion of interest and further innovation in this field."

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The article "Fast and sensitive bolometric terahertz detection at room temperature through thermomechanical transduction" is published in the Journal of Applied Physics at doi: 10.1063/1.5045256.

About Institute of Industrial Science (IIS), the University of Tokyo

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More than 120 research laboratories, each headed by a faculty member, comprise IIS, with more than 1,000 members including approximately 300 staff and 700 students actively engaged in education and research. Our activities cover almost all the areas of engineering disciplines. Since its foundation in 1949, IIS has worked to bridge the huge gaps that exist between academic disciplines and real-world applications.

Abstract-Fast and sensitive bolometric terahertz detection at room temperature through thermomechanical transduction

Journal of Applied Physics

 Ya Zhang, Suguru Hosono, Naomi Nagai, Sang-Hun Song,  Kazuhiko Hirakawa

(a) Wafer structure used to fabricate the doubly clamped GaAs beam resonator. (b) Schematic illustration of the GaAs beam resonator fabricated by selective etching. (c) Microscope image of a fabricated GaAs MEMS beam resonator (100 × 30 × 1.2 μm3). The 2DEG layer and the top gates on both ends of the beam form two piezoelectric capacitors, C1 and C2. A 15-nm-thick NiCr THz absorbing layer was deposited on the beam. This metal film was also used as a heater to calibrate the thermal responsivity of the resonator. (d) The resonance spectra measured by sweeping the driving frequency at various input heating powers, Pin, from 0 μW to ∼1100 μW. The red curve is the resonance spectrum at Pin = 0. (e) Normalized frequency shift as a function of Pin.

https://aip.scitation.org/doi/abs/10.1063/1.5045256

Terahertz (THz) electromagnetic spectrum draws wide attention for nondestructive and/or biocompatible sensing. In order to be widely applicable to the THz sensing, it is of prime importance to develop THz sensors that can be operated at room temperature and have high sensitivity and fast operation speed. However, conventional room-temperature THz thermal sensors fall short of expectations in these characteristics required in various applications of THz sensing, including THz cameras. Utilizing a thermomechanical transduction scheme, we have developed an uncooled, sensitive, and fast THz bolometer by using a doubly clamped GaAs microelectromechanical system (MEMS) beam resonator as a sensitive thermistor. Owing to its ultrahigh temperature sensitivity (the noise equivalent temperature difference of ∼1 μK/√Hz), the present bolometer achieves not only high sensitivity but also an operation bandwidth of several kHz, which is more than 100 times faster than other uncooled THz thermal sensors. The obtained electrical noise equivalent power is as low as ∼90 pW/√Hz, which is close to the limit set by the thermal fluctuation noise. The MEMS bolometers are fabricated by the standard semiconductor fabrication processes and are well suited for making detector arrays for realizing THz cameras.

Abstract-Terahertz dynamics of electron–vibron coupling in single molecules with tunable electrostatic potential

Shaoqing Du, Kenji Yoshida, Ya Zhang, Ikutaro Hamada, Kazuhiko Hirakawa,

https://www.nature.com/articles/s41566-018-0241-1

Clarifying electronic and vibronic properties at the individual molecule level provides key insights for future chemistry, nanoelectronics and quantum information technologies. However, information obtained by conventional single-molecule transport measurements is based on time-averaged properties. Here, we report on terahertz (THz) spectroscopy of single fullerene molecules by using a single-molecule transistor geometry. From the time-domain THz autocorrelation measurements, we obtained THz spectra associated with the THz-induced centre-of-mass oscillation of the molecules. The observed spectra reflect the potential profile experienced by the molecule on the metal surface when the number of electrons on the molecule fluctuates by one during the single-electron tunnelling process. Such an ultra-high sensitivity to the electronic/vibronic structures of a single molecule on the addition/removal of a single electron has been achieved as a result of using THz spectroscopy in the single-molecule transistor geometry. This scheme provides an opportunity to investigate the ultrafast THz dynamics of subnanometre-scale systems.

Abstract-Terahertz Intersublevel Transitions in Single Self-Assembled InAs Quantum Dots with Variable Electron Numbers

Ya Zhang *†, Kenji Shibata †‡, Naomi Nagai †, Camille Ndebeka-Bandou †§, Gerald Bastard †§, and Kazuhiko Hirakawa *†‡

†Center for Photonics Electronics Convergence, Institute of Industrial Science and ‡Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

§ Laboratoire Pierre Aigrain, Ecole Normale Superieure, 24 rue Lhomond F75005, Paris, France

Nano Lett., Article ASAP

DOI: 10.1021/nl5042319

Publication Date (Web): January 12, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl5042319

We propose a method for performing terahertz spectroscopy on nanometer (nm)-scale systems by using metal nanogap electrodes. Intersublevel transition spectra of single self-assembled InAs quantum dots (QDs) have been measured with high signal/noise ratios by using a single electron transistor geometry that consists of a QD and nanogap metal electrodes as a terahertz detector. Photocurrent distribution with respect to the Coulomb diamonds indicates that there are two mechanisms for the photocurrent generation. When the p shell was fully occupied, we observed rather simple photocurrent spectra induced by the p → d transitions. However, when the p shell was half-filled, the photocurrent spectra exhibited a markedly different behavior, which we attribute to the fluctuation in electron configuration when the empty p state is filled back from the electrodes.

Keywords: 

Terahertz spectroscopy; nanostructures; intersublevel transitions; quantum dots; nanometer-scale spectroscopy

Abstract-Terahertz intersublevel transitions in single self-assembled InAs quantum dots with variable electron numbers

Ya Zhang , Kenji Shibata , Naomi Nagai , Camille Ndebeka-Bandou , Gerald Bastard , and Kazuhiko Hirakawa

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl5042319

Publication Date (Web): January 12, 2015

Copyright © 2015 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl5042319?journalCode=nalefd

We propose a method for performing terahertz spectroscopy on nanometer (nm)-scale systems by using metal nanogap electrodes. Intersublevel transition spectra of single self-assembled InAs quantum dots (QDs) have been measured with high signal/noise ratios by using a single electron transistor geometry that consists of a QD and nanogap metal electrodes as a terahertz detector. Photocurrent distribution with respect to the Coulomb diamonds indicates that there are two mechanisms for the photocurrent generation. When the p shell was fully occupied, we observed rather simple photocurrent spectra induced by the p→d transitions. However, when the p shell was half-filled, the photocurrent spectra exhibited a markedly different behavior, which we attribute to the fluctuation in electron configuration when the empty p state is filled back from the electrodes.

Abstract-MEMS reconfigurable metamaterial for terahertz switchable filter and modulator

Zhengli Han, Kenta Kohno, Hiroyuki Fujita, Kazuhiko Hirakawa, and Hiroshi Toshiyoshi  »View Author Affiliations

Optics Express, Vol. 22, Issue 18, pp. 21326-21339 (2014)
http://dx.doi.org/10.1364/OE.22.021326

We demonstrate a reconfigurable metamaterial developed by surface micromachining technique on a low loss quartz substrate for a tunable terahertz filter application. The device implements a reconfigurable RF-MEMS (radio frequency – micro electro mechanical systems) capacitor within a split-ring resonator (SRR). Time-domain spectroscopy confirms that the tunability of the SRR resonance and thus the terahertz transmittance are electrostatically controlled by the RF-MEMS capacitor. Due to the high transparency and low loss of quartz used as a substrate, the device exhibits a high contrast switching performance of 16.5 dB at 480 GHz, which is also supported by the terahertz dynamic modulation measurement results. The device shows promise for tunable transmission terahertz optics.

© 2014 Optical Society of America