Room Temperature Operation Research Articles

Laser Cooling Assisted Thermal Management of Lightsails

A lightsail can be accelerated to ultra-high speed by the radiation pressure of a laser having an intensity of the order of GW/m$^2$, which though presents a critical challenge in the thermal management of lightsails. In this letter, we explore the applicable regimes of solid-state laser cooling in dissipating heat in additional to the previously explored radiative cooling approach. We begin by examining the cooling capacity of laser cooling, and show that the cooling rate from a micron-thick layer doped with ytterbium ions can exceed that of blackbody thermal emission. This allows more intense laser illumination upon material damage, and consequently shortened acceleration distance. Next, we explore the impact of the limited operating bandwidth of laser cooling to account for the Doppler shift of the pumping laser, and conclude that laser cooling is helpful for target velocities $\lesssim5\%$ for room-temperature operations.

Enzyme-free and isothermal discrimination of microRNA point mutations using a DNA split proximity circuit with turn-on fluorescence readout

MicroRNAs (miRNAs) hold immense potential as disease biomarkers, yet their short lengths and high sequence homology pose unique challenges in detection. Conventional methods such as the gold standard qRT-PCR and other isothermal amplification methods require sophisticated primer designs and use of enzymes which add uncertainties to the assay robustness. In this work, we demonstrate the use of a plug-and-play molecular detection platform, termed split proximity circuit (SPC), to achieve a selectivity comparable to qRT-PCR in differentiating point mutations using several miRNAs as proof-of-concept models. The analytical sensitivity of SPC has been improved by a hundred-fold over our previous work and matches/outperforms the enzyme-free assays reported in the literature by evolving the core signal-generating domains. Key design changes include improved hybridization chain reaction (HCR) hairpin sequences and the incorporation of a turn-on fluorescence signal based on fluorophore-quencher format. The core domains were then kept constant while redesigning the target recognition region to be complementary to various target sequences, all of which yield similar analytical performance. Notably, SPC maintained robust signal recovery with low variance even in complex biological matrices. With its enzyme-free and single room temperature operation, SPC presents a promising platform for quick and easy miRNA quantification.

High Power Mid-Infrared Quantum Cascade Lasers Grown on Si

This article details the demonstration of a strain-balanced, InP-based mid-infrared quantum cascade laser structure that is grown directly on a Si substrate. This is facilitated by the creation of a metamorphic buffer layer that is used to convert from the lattice constant of Si (0.543 nm) to that of InP (0.587 nm). The laser geometry utilizes two top contacts in order to be compatible with future large-scale integration. Unlike previous reports, this device is capable of room temperature operation with up to 1.6 W of peak power. The emission wavelength at 293 K is 4.82 μm, and the device operates in the fundamental transverse mode.

Ultra-high-resolution quanta image sensor with reliable photon-number-resolving and high dynamic range capabilities

Superior low-light and high dynamic range (HDR) imaging performance with ultra-high pixel resolution are widely sought after in the imaging world. The quanta image sensor (QIS) concept was proposed in 2005 as the next paradigm in solid-state image sensors after charge coupled devices (CCD) and complementary metal oxide semiconductor (CMOS) active pixel sensors. This next-generation image sensor would contain hundreds of millions to billions of small pixels with photon-number-resolving and HDR capabilities, providing superior imaging performance over CCD and conventional CMOS sensors. In this article, we present a 163 megapixel QIS that enables both reliable photon-number-resolving and high dynamic range imaging in a single device. This is the highest pixel resolution ever reported among low-noise image sensors with photon-number-resolving capability. This QIS was fabricated with a standard, state-of-the-art CMOS process with 2-layer wafer stacking and backside illumination. Reliable photon-number-resolving is demonstrated with an average read noise of 0.35 e- rms at room temperature operation, enabling industry leading low-light imaging performance. Additionally, a dynamic range of 95 dB is realized due to the extremely low noise floor and an extended full-well capacity of 20k e-. The design, operating principles, experimental results, and imaging performance of this QIS device are discussed.

High-Temperature Annealing Effects on Atomically Thin Tungsten Diselenide Field-Effect Transistor

Two-dimensional (2D) material-based devices are expected to operate under high temperatures induced by Joule heating and environmental conditions when integrated into compact integrated circuits for practical applications. However, the behavior of these materials at high operating temperatures is obscure as most studies emphasize only room temperature or low-temperature operation. Here, the high-temperature electrical response of the tungsten diselenide (WSe2) field-effect transistor was studied. It is revealed that 350 K is the optimal annealing temperature for the WSe2 transistor, and annealing at this temperature improves on-current, field-effect mobility and on/off ratio around three times. Annealing beyond this temperature (360 K to 670 K) adversely affects the device performance attributed to the partial oxidation of WSe2 at higher temperatures. An increase in hysteresis also confirms the formation of new traps as the device is annealed beyond 350 K. These findings explicate the thermal stability of WSe2 and can help design 2D materials-based durable devices for high-temperature practical applications.

Electromagnetically induced transparency based quantum well infrared photodetectors

The characteristics of quantum well infrared photodetectors (QWIPs) which utilizing electromagnetically induced transparency (EIT) have been presented in this communication. Instead of direct absorption and creation of photoelectrons by the long wavelength infrared signal, the absorption properties of a short wavelength probe is modified by the infrared signal which subsequently creates photoelectrons. Owing to the indirect creation of photocurrent, the component of dark current which is due to thermionic emission is eliminated, thereby decreasing total dark current appreciably. The value of photocurrent depends on infrared signal power, bias voltage, probe detuning, and Rabi frequency of the control field. Results of this investigation may find potential applications in the development of terahertz infrared quantum well photodetectors under room temperature operation.

Lower threshold current density of GaN-based blue laser diodes by suppressing the nonradiative recombination in a multiple quantum well.

The influence of the nonradiative recombination in a multiple quantum well of GaN-based blue laser diodes (LDs) has been are studied experimentally and theoretically by analyzing the optical and electrical properties of LDs with various thickness and indium content of quantum wells (QWs). It is found that when keeping the LD emission wavelength nearly unchanged, the LD device performance with thinner QW and higher indium content of InGaN QWs is much better than the LD with thicker QW and lower indium content, having smaller threshold current density, higher output optical power and larger slope efficiency. Typically, the threshold current density is as low as 0.69 kA/cm2, and the corresponding threshold current is only 250 mA. The lifetime is more than 10,000 hours at a fixed injection current of 1.2 A under a room-temperature continuous-wave operation. Characteristics of photoluminescence (PL) microscopy images, temperature dependent PL spectra, time-resolved PL and electroluminescence spectra demonstrate that a reduction of the nonradiative recombination centers and an improvement of homogeneity in QWs are the main reason for the performance improvement of GaN-based LD using thinner QW layers with a higher indium content in a certain range. Moreover, theoretical calculation results demonstrate that using a thinner quantum well is also helpful for improving the device performance if the change of alloy material quality is considered during the calculation.

Demonstration of room-temperature continuous-wave operation of InGaAs/AlGaAs quantum well lasers directly grown on on-axis silicon (001)

Room-temperature continuous-wave operation of InGaAs/AlGaAs quantum well lasers directly grown on on-axis silicon (001) has been demonstrated. A 420 nm thick GaAs epilayer completely free of antiphase domains was initially grown on the silicon substrate in a metal-organic chemical vapor deposition system and the other epilayers, including four sets of five-period strained-layer superlattices and the laser-structural layers, were successively grown in a molecular beam epitaxy system. The lasers were prepared as broad-stripe Fabry–Pérot ones with a stripe width of 21.5 μm and a cavity length of 1 mm. Typically, the threshold current and the corresponding threshold current density are 186.4 mA and 867 A/cm2, respectively. The lasing wavelength is around 980 nm, and the slope efficiency is 0.097 W/A with a single-facet output power of 22.5 mW at an injection current of 400 mA. This advancement makes the silicon-based monolithic optoelectronic integration relevant to quantum well lasers more promising with an enhanced feasibility.

Room Temperature Operating, Fast and Reusable Polyaniline Sensor Synthesized Ultrasonically Using Organic and Inorganic Acid Dopants

In this paper we report a simple, green method for synthesis of polyaniline (PANI) nanoparticles by chemical oxidative polymerization with the assistance of ultrasonic irradiation. The polyaniline nanomaterials were synthesized with several organic acid dopants (tartaric acid (C4H6O6) and oxalic acid (C2H2O4)) and inorganic acid dopants (hydrochloric acid (HCl) and perchloric acid (HClO4)). A comparative study of the effect of the organic and inorganic acid dopants on the sensing properties of PANI for ammonia (NH3) vapors at room temperature was performed. It was observed that the electrical properties of the doped PANI depended on the type of the acid dopant. A remarkable change in resistance was observed upon doping with the different acid dopants. Structural and morphological studies and composition analysis were performed by UV-visible, FTIR, XRD and SEM techniques. The highest conductivity was obtained for PANI with HClO4 acid dopant while the lowest conductivity was obtained for PANI with tartaric acid dopant. The results showed that PANI doped with tartaric acid was an excellent sensor with fast response time and an enhanced sensitivity (26.1% for 5 ppm and 56% for 100 ppm) for NH3 gas at room temperature. PANI doped with organic acids showed faster recovery following NH3 treatment as compared to PANI doped with inorganic acid dopants. The PANI doped with tartaric acid sensor showed excellent stability for 350 days. In summary ultrasonic irradiation and the nature of the dopants showed significant effects on enhancing the sensing performance.

In2O3/g-C3N4/Au ternary heterojunction-integrated surface plasmonic and charge-separated effects for room-temperature ultrasensitive NO2 detection

Light-activated gas sensors based on semiconducting metal oxides (SMOs) hold great promise for next-generation gas sensing application, due to their unique superiority including room-temperature operation, intrinsic safety, and simple device structure. However, poor visible-light absorption and fast carrier recombination of SMOs sensing film are two main barriers that seriously restrict their sensing performance of light-activated gas sensors. Herein, a visible-light activated gas sensor based on Au nanoparticles modified In2O3/g-C3N4 heterojunction nanofibers is developed. Excellent sensing response (Rg/Ra = 17.2 to 1 ppm NO2, where Ra and Rg represent the resistance of sensors when exposed to air or target gas) and fast response/recovery kinetics at room temperature are obtained, which is markedly better than the sensors based on pristine In2O3 nanofibers and In2O3/g-C3N4 nanofibers. Through the discussion and estimation of experimental results, the improved gas sensing properties of In2O3/g-C3N4/Au-based sensors are speculated to be related to the enhanced visible light utilization benefiting from localized surface plasmon resonance (LSPR) effect of Au nanoparticles, and the efficient separation of photo-generated carriers enabled by heterojunctions between In2O3, Au, and g-C3N4 components. The current work will provide a universal strategy to develop high-performance light-activated gas sensor and a deep understanding about the sensing principle of this novel type of gas sensor.

Selectively-Grown Quantum Dot Active Region Lasers

Nanopatterns formed by dense nanoscale (20–30nm diameter) block copolymer lithography and subsequent selective area MOVPE were utilized to realize room temperature operation of quantum dot (QD) active region laser diodes on InP substrates, by employing a carrier-injection layer adjacent to the QDs. Initial studies focused on InGaAs QDs grown on GaAs substrates, which exhibit relatively broad photoluminescence (PL) emission linewidths (FWHM~93meV at RT). Atomic force microscopy measurements reveal that a wide distribution of QD thickness variations correlates well to the observed broad PL linewidths, based on the simulated range of QD transitions. The fabricated edge-emitting devices on InP substrate exhibit lasing emission near <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.57\sim 1.67~\mu \text{m}$ </tex-math></inline-formula> at room temperature with a threshold current density as low as 1.6 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for 4mm-long devices. The observed dependency of device characteristics, such as threshold current density and lasing wavelength, on the cavity length and on the heat sink temperature suggests the dominant lasing transition energy corresponds to the QD excited state, except for the longest cavity length devices (L = 4mm) which operate on the QD ground state transition near room temperature. We believe these data represent the only reports of lasers in this wavelength region employing QDs formed by diblock co-polymer lithography and selective area MOVPE growth. These data also suggest that QD height variations need to be further reduced, through MOVPE growth optimization, to achieve higher optical gain from the QD ground state transition.

Mach-Zehnder interferometer based integrated-photonic acetone sensor approaching the sub-ppm level detection limit.

The detection of acetone in the gaseous form in exhaled breath using an integrated sensor can provide an effective tool for disease diagnostics as acetone is a marker for monitoring human metabolism. An on-chip acetone gas sensor based on the principle of Mach-Zehnder interferometer is proposed and demonstrated. The sensing arm of the device is activated with a composite film of polyethyleneimine and amido-graphene oxide as the gas-sensitive adsorption layer. The composite film demonstrates good selectivity to acetone gas, can be used repeatedly, and is stable in long-term use. Room temperature operation has been demonstrated for the sensor with high sensitivity under a 20 ppm acetone environment. The detection limit can reach 0.76 ppm, making it feasible to be used for the clinical diagnosis of diabetes and the prognosis of heart failure.

Microdisk array based Weyl semimetal nanofilm terahertz detector

Abstract High-performance terahertz wave detectors at room temperature are still urgently required for a wide range of applications. The available technologies, however, are plagued by low sensitivity, narrow spectral bandwidth, complicated structure, and high noise equivalent power (NEP). Here, we have demonstrated a Weyl semimetal surface plasmon-enhanced high-performance terahertz wave detectors which are based on microdisk array deposited WTe2 nanofilm epitaxially grown on GaN substrate for room temperature operation. With the microdisk array combined the WTe2 layer, strong terahertz wave surface plasmon polaritons can be generated at the WTe2–air interfaces, which results in significant improvement in detecting performance. For the 40 μm diameter microdisk array, a detectivity (D *) of 5.52 × 1012 cm Hz1/2 pW−1 at 0.1 THz is achieved at room temperature. In addition, the responsivity (R A) of 8.78 A W−1 is also obtained. Such high-performance millimeter and terahertz wave photodetectors are useful for wide applications such as high capacity communications, walk-through security, biological diagnosis, spectroscopy, and remote sensing.

Ultra-wide-band millimeter-wave generator using spin torque oscillator with strong interlayer exchange couplings

Recent increased development interest in millimeter-wave oscillator devices has necessitated realization of small oscillators with high frequency, wide frequency tunability, and room-temperature operation. Spin-torque oscillators (STOs) are fascinating candidates for such applications because of their nanometer size and suitability for room-temperature operation. However, their oscillation frequency and tunable range are limited to the order of 100 MHz–10 GHz. Here, we propose use of bilinear (J1) and biquadratic (J2) interlayer exchange couplings between ferromagnets in STOs to overcome these problems. The bilinear coupling contributes to oscillation frequency enhancement, whereas the biquadratic coupling facilitates frequency tunability via a current. Using micromagnetic simulation with parameters estimated from a material with small saturation magnetization, for J1 = 0 and J2 = − 1.0 mJ/m2, respectively, we find that the STO exhibits high frequency from 23 to 576 GHz and that its tunability reaches 61 GHz/(1011 A/m2) for current densities of − 0.5 to − 9.5 × 1011 A/m2. An analytical theory based on the macrospin model is also developed, which exhibits good quantitative agreement with the micromagnetic simulations. These results introduce new possibilities for spintronics applications in high-frequency devices such as next-generation mobile communications.

(Invited, Digital Presentation) Silicon Compatible Quantum Computers: Challenges in Devices, Integration, and Circuits

Quantum computers have been attractive because they could realize large-scale and highly complicated calculations that conventional computers cannot solve within a finite time. The large-scale integration of qubits, which are the building block of quantum computers, is required to realize their practical application. Indeed, fault-tolerant quantum computers require the integration of one million qubits. Therefore, silicon qubits is a high-profile candidate because they have advanced process and miniaturization technologies developed with VLSI. In addition, silicon qubits are advantageous in operation temperature. Superconductor qubits operate at the cryogenic temperature at around a few tens mK; in contrast, the operation principle of silicon qubits can operate at a much higher temperature over 1 K. The high-temperature operation can realize quantum computers with small and high-power refrigerators; therefore, we can expect desktop quantum computers instead of ongoing supercomputer-size ones. We must promote integration technology development for silicon qubits; however, the silicon qubit research was mainly in the physics field. Then, nowadays, the integration technology development is accelerated in the world.The challenges are in all conventional research fields: devices, integration, and circuits. We must re-develop the silicon technologies for quantum. For example, on the device design, now we do not have a good tool to design the qubits like TCAD; therefore, we must re-develop the TCAD technologies for quantum [1]. Actually, this is the starting point of our recent research activities; we are going to develop a quantum device simulator, clarify the requirements on the fabrication process of silicon qubits, and propose new technologies to reduce the variability to realize large-scale integration [2]. As for the integration, the quantum calculation circuits require several integrated items: qubits, qubit couplers, micro-magnets, and readout systems. The situation is quite different from the conventional VLSI case for which only the transistors should be integrated. Therefore, we must go re-developing new technologies to integrate all these items. Regarding the circuits, we must use CMOS circuits to generate input signals for qubits and readout the results of quantum calculation, which should be operated at cryogenic temperature. This is so-called “cryo-CMOS.” We must explore a new side of the transistor technologies, which is not investigated so far, because the physics of the MOSFET operation is quite different from the conventional room-temperature operation, hampering the circuit design due to the lack of the device operation model. In this situation, despite the long history of MOSFETs, new phenomena of transistor operation are discovered. For example, the low-frequency current noise increases at a low temperature. The origin of the noise is on the interface traps, instead of the fixed charges in the gate oxides as is the case for room temperature operation [3]. Therefore, we must re-developing CMOS circuit technologies from the bottom of the technologies, device physics.In this presentation, I’m going to overview the status of silicon technology developments for quantum from the viewpoints of devices, integration, and circuits. Also, we introduce some of our recent results to contribute to the developments.Acknowledgment: Our work is supported by MEXT Quantum Leap Flagship Program (Q-LEAP) JPMXS0118069228.[1] H. Asai et al., IEEE Electron Devices Technology and Manufacturing Conference 2021.[2] S. Iizuka et al., Tech. Dig. Symp. VLSI Technology 2021.[3] H. Oka et al., Tech. Dig. Symp. VLSI Technology 2020.

Historical Perspectives, State of Art and Research Trends of SPAD Arrays and Their Applications (Part II: SPAD Arrays)

The ability to detect single photons is becoming an enabling key capability in an increasing number of fields. Indeed, its scope is not limited to applications that specifically rely on single photons, such as quantum imaging, but extends to applications where a low signal is overwhelmed by background light, such as laser ranging, or in which faint excitation light is required not to damage the sample or harm the patient. In the last decades, SPADs gained popularity with respect to other single-photon detectors thanks to their small size, possibility to be integrated in complementary metal-oxide semiconductor processes, room temperature operability, low power supply and, above all, the possibility to be fast gated (to time filter the incoming signal) and to precisely timestamp the detected photons. The development of large digital arrays that integrates the detectors and circuits has allowed the implementation of complex functionality on-chip, tailoring the detectors to suit the need of specific applications. This review proposes a complete overview of silicon SPADs characteristics and applications. In the previous Part I, starting with the working principle, simulation models and required frontend, the paper moves to the most common parameters adopted in literature for characterizing SPAD performance and describes single pixels applications and their performance. In this Part II, the focus is posed on the development of SPAD arrays, presenting some of the most notable examples found in literature. The actual exploitation of these designs in real applications (e.g., automotive, bioimaging and radiation detectors) is then discussed.

Optical Terahertz Sources Based on Difference Frequency Generation in Nonlinear Crystals

Terahertz (THz) sources, ranging from 0.1 THz to 10 THz, between microwaves and infrared waves, have important applications in spectral detection, medical imaging, communication, etc. Difference frequency generation (DFG) is an effective method for generating terahertz with the characteristics of low cost, simple structure, widely tunable range, no threshold, and room-temperature operation. This paper reviews various optical terahertz sources of difference frequency generation based on nonlinear crystals, including DFG with inorganic crystals, DFG with organic crystals, DFG with quasi-phase-matching (QPM) crystals, DFG in waveguides, cavity-enhanced DFG, and cascaded DFG. Their recent advances, as well as their advantages and disadvantages, are fully present and discussed. This review is expected to provide a comprehensive reference for researchers in this field and a quick understanding of optical THz sources of difference frequency generation with nonlinear crystals.

Historical Perspectives, State of art and Research Trends of Single Photon Avalanche Diodes and Their Applications (Part 1: Single Pixels)

The ability to detect single photons is becoming an enabling key capability in an increasing number of fields. Indeed, its scope is not limited to applications that specifically rely on single photons, such as quantum imaging, but extends to applications where a low signal is overwhelmed by background light, such as laser ranging, or in which faint excitation light is required not to damage the sample or harm the patient. In the last decades, SPADs gained popularity with respect to other single-photon detectors thanks to their small size, possibility to be integrated in Complementary Metal-Oxide Semiconductor processes, room temperature operability, low power supply and, above all, the possibility to be fast gated (to time filter the incoming signal) and to precisely timestamp the detected photons. The development of large digital arrays that integrates the detectors and circuits has allowed the implementation of complex functionality on-chip, tailoring the detectors to suit the need of specific applications. This review proposes a complete overview of silicon SPADs characteristics and applications. In this Part I, starting with the working principle, simulation models and required frontend, the paper moves to the most common parameters adopted in literature for characterizing SPADs, and describes single pixels applications and their performance. In the next Part II, the focus is then posed on the development of SPAD arrays, presenting some of the most notable examples found in literature. The actual exploitation of these designs in real applications (e.g., automotive, bioimaging and radiation detectors) is then discussed.

Oscillator-Network-Based Ising Machine.

With the slowdown of Moore’s law, many emerging electronic devices and computing architectures have been proposed to sustain the performance advancement of computing. Among them, the Ising machine is a non-von-Neumann solver that has received wide attention in recent years. It is capable of solving intractable combinatorial optimization (CO) problems, which are difficult to be solve using conventional digital computers. In fact, many CO problems can be mapped to finding the corresponding ground states of Ising model. At present, Ising machine prototypes based on different physical principles, such as emerging memristive oscillators, have been demonstrated, among which the Ising Hamiltonian solver based on the coupled oscillator network simultaneously holds the advantages of room-temperature operation, compact footprint, low power consumption, and fast speed to solution. This paper comprehensively surveys the recent developments in this important field, including the types of oscillators, the implementation principle of the Ising model, and the solver’s performance. Finally, methods to further improve the performance have also been suggested.

Emergence of MXene–Polymer Hybrid Nanocomposites as High‐Performance Next‐Generation Chemiresistors for Efficient Air Quality Monitoring

AbstractAir contamination is one of the foremost concerns of environmentalists worldwide, which has elevated global public health concerns for monitoring air contaminants and implementing appropriate safety policies. These facts have generated nascent global demand for exploring sustainable and translational strategies required to engineer affordable, intelligent, and miniaturized sensors because commercially available sensors lack lower detection limits, room temperature operation, and poor selectivity. The state‐of‐the‐art sensors are concerned with architecting advanced nanomaterials to achieve desired sensing performance. Recent studies demonstrate that neither pristine metal carbides/nitrides (MXenes) nor polymers (P) can address these practical challenges. However, synergistic combinations of various precursors as hybrid‐nanocomposites (MXP‐HNCs) have emerged as superior sensing materials to develop next‐generation intelligent environmental, industrial, and biomedical sensors. The expected outcomes could be manipulative due to optimizing physicochemical and morphological attributes like tunable interlayer‐distance, optimum porosity, enlarged effective surface area, rich surface functionalities, mechanical flexibility, and tunable conductivity. This review intends to detail a comprehensive summary of the advancements in state‐of‐the‐art MXP‐HNCs chemiresistors. Moreover, the underlying sensing phenomenon, chemiresistor architecture, and their monitoring performance are highlighted. Besides, an overview of challenges, potential solutions, and prospects of MXP‐HNCs as next‐generation intelligent field‐deployable sensors with the integration of IoT and AI are outlined.