Metal Diodes Research Articles

Optimized polarization-independent Chand-Bali nano-antenna for thermal IR energy harvesting

A novel, polarization-independent, wide-angle reception Chand-Bali nano-antenna is proposed. An adjoint-based optimization algorithm is used to create the same resonance at both linear polarizations of the incident radiation. The nano-antenna optimal parameters reveal that two hot spots with a strong field enhancement are created. These hot-spots could be integrated with metal–insulator–metal (MIM) diodes to form a rectenna for infrared (IR) energy harvesting. The metallic resonators allow for selecting several materials to facilitate the fabrication of the nano-antenna and the MIM diode. The Chand-Bali-based IR rectennas are investigated and simulations demonstrate an improvement of more than one order of magnitude in efficiency compared to ones using traditional nano-antennas.

Electron affinity of metal oxide thin films of TiO2, ZnO, and NiO and their applicability in 28.3 THz rectenna devices

The holy grail of achieving efficient operation of infrared (IR) rectennas continues to be the realization of a high performance rectifier. In this paper, we have fabricated metal–insulator–metal (MIM) diodes based on TiO2, ZnO, and NiO thin films using shadow mask evaporation, photolithography, and sputtering. The electron affinities of oxides have been measured by a combination of variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy, as well as deduction from the extraction of metal/oxide barrier heights of Fowler–Nordheim tunneling plots. Our results confirm a low value for the electron affinity of NiOx of ∼2.1–2.5 eV, which correlates with the high zero-bias dynamic resistance (RD0) of ∼500 kΩ of an associated MIM diode. These values render NiOx to be unsuitable for use in a rectenna device. Better performance has been observed from diodes based on TiO2 and ZnOx films. The best rectification performance was achieved for a Au/2.6 nm ZnOx/Cr diode, scaled down to 1 μm2 device area, showing a zero-bias dynamic resistance of RD0 = 71 kΩ, zero-bias responsivity β0 = 0.28 A/W, and a coupling efficiency of ηc = 2.4 × 10−5% for rectification at 28.3 THz. The main significance of this study is that it employs a methodology whereby key parameters of the MIM stack are derived from physical measurements, which are then used to assist in the fitting of electrical current–voltage data to produce a reliable appraisal of diode performance in an IR rectenna.

First-principles investigation of interface phenomena in hafnium-based metal–insulator–metal diodes

First-principles investigation of interface phenomena in hafnium-based metal–insulator–metal diodes

Length-dependent high-frequency response of aromatic and aliphatic molecules: predictions from first-principles calculations

Quantum capacitance and quantum transport calculations are conducted using density functional theory in combination with nonequilibrium Green’s functional formalism to predict the effect of length on high-frequency response of aromatic molecules with different number of oligophenyl groups (n = 1, 2, 3) sandwiched between gold (111) electrodes through thiol and mercaptomethyl thiol anchoring groups. The results show that the quantum capacitance of the junctions decreases linearly with the length of the molecule regardless of the type of the edge group. The cutoff frequency of the molecular junctions show exponential decay as a function of the length in the THz frequency range. The insertion of the methylene group decreases the cutoff frequency by more than an order of magnitude due to enhanced differential resistance. We have also studied the high frequency response of aliphatic molecular junctions with different lengths and found that the cutoff frequencies of these structures are orders of smaller than the ones for the aromatic molecular junctions. These findings can be of practical importance in developing metal–molecule–metal diodes for high-frequency applications.

Enhanced current density and asymmetry of metal–insulator–metal diodes based on self-assembly of Pt nanoparticles

Metal–insulator–metal (MIM) diodes facilitate rectification at high frequencies. However, the rectification ratio for light from visible to infrared spectra is insufficient. In this study, we developed a MIM diode with a strongly enhanced electric field achieved using the self-assembly of Pt nanoparticles (NPs) via atomic layer deposition. By shaping the tunneling barrier, current density and asymmetry were simultaneously enhanced by several orders of magnitude compared with the symmetric MIM diode. The diode efficiency of the proposed MIM diodes was experimentally demonstrated to be 231 times greater than that of the MIM diode without NPs. This strategy indicates significant potential for high-frequency rectification applicable in optical rectenna.

Parallel metal–insulator–metal diode with an ultrathin spin-coated hydrogen silsesquioxane insulating layer

In this study, we investigated a parallel metal–insulator–metal (MIM) diode with an ultrathin spin-coated hydron silsesquioxane (HSQ) layer. Ti and Au were adopted as the metal electrodes for the large work function difference. Conditions to obtain the ultrathin HSQ layer with a thickness of below 5 nm for tunneling were predicted and Ti/HSQ/Au diode devices with a parallel electrode arrangement were fabricated by using the conditions. The typical current–voltage characteristics of the fabricated diodes exhibited asymmetry of about 1.8 at 3.0 V. It was demonstrated that the dynamic zero bias resistance of the diodes was as low as about 8 MΩ. Based on the Simmons model, the estimated oxide-equivalent thickness of HSQ in the device was about 1.7 nm, which was in good agreement with the prediction. The good figures of merit of the fabricated diodes imply that the spin-coated ultrathin HSQ is very suitable for this application.

First-principles investigation of interface phenomena in hafnium-based metal-insulator-metal diodes.

Metal-insulator-metal (MIM) diodes are very interesting in many different applications exploiting environment-friendly renewable energy solutions. Moreover, since the dimensions of such devices are at the nanoscale, the size and the characteristics of their constitutive elements can drastically influence their macroscale performance. As it could be difficult to describe in detail the physical phenomena occurring among materials in nanoscale systems, in this work first-principles calculations have been used to study the structural and electrical properties of three different hafnium oxide (HfO2)-MIM diodes. These devices have been simulated at the atomistic level by interposing 3 nm of HfO2 between drain and source electrodes made of gold and platinum, respectively. The monoclinic and orthorhombic polymorphs of HfO2 have been considered to model different types of MIM diodes, and the interface geometries have been optimized to compute the current-voltage characteristics, reflecting the tunneling mechanisms occurring in such devices. The calculation of the transmission pathways has also been carried out to investigate the effects of atomistic coordinates despite the use of the same material. The results demonstrate the role of the Miller indices of metals and the influence of the HfO2 polymorphs on the MIM properties. In this study, the importance of interface phenomena on the measurable properties of the proposed devices has been investigated in detail.

Study of Electrochemical Properties of Compared Indigo for Metal–Semiconductor–Metal Diode

Indigo blue was discovered as a semiconductor material because of its organic semiconductor properties. This paper shows a primary study of the electrochemical properties of Sakon Nakhon-indigo strain used in the metal–semiconductor–metal (MSM) diode. The fermentation and extraction of our local indigo plant are explained. Indian indigo in the MSM diode is compared in the same conditions of preparation. The electrochemical properties, including the current–voltage (I–V) characteristic, static resistance, and rectification ratio, are discussed. The results show that the electron and hole characteristics and band gap energy of the indigo blue affects the electrochemical properties of the device. Our local MSM diode has a suitable operation between −1 and +3 VMSM with a knee voltage of 1.0 VMSM. Especially, it can produce the highest forward-bias current of about 3.19 mA at linear operation between +2 and +3 VMSM, whereas the review MSM diode is about 2–3 hundred times lower. This shows that this strain has more conductive properties because of its effective electron and hole characteristics obtained by an indigo yield concentration. Therefore, the MSM diode based on Sakon Nakhon-indigo strain is an important role in an electronic semiconductor device for low voltage consumption and high sensitivity. In the future, the molecular characteristics of local indigo may be deeply analyzed to be further developed into a thin-film form used as an organic semiconductor material in several electronic devices.

Impact of Metal Work-Function on Current Rectification by Metal-Insulator-Metal Diodes

This article presents the experimental investigation of the effect of metal work-function on current rectification by metal–insulator–metal (MIM) diodes. Diverse MIM diode topologies that utilized various types of metal configurations were fabricated and subjected to DC electrical (J-V) characterization, and it was found that the work-function of the various metals impacts the symmetry and linearity of the diodes’ current–voltage curves, the amount of current the diodes can rectify, and their typical zero-bias curvature coefficients. The diodes whose both metal layers have the same work-function exhibits more linear and symmetrical current–voltage curves, with the curves becoming more non-linear and asymmetrical as the variation in work-function of the metals increase, impacting the applications where MIM diodes can be used.

High-Performance Atomic Layer Deposited Al2O3 Insulator Based Metal-Insulator-Metal Diode

The fabrication of metal–insulator– metal (MIM) diode using an ultrathin Al2O3 insulator layer, deposited using atomic layer deposition (ALD) is presented. The Al2O3 insulating layer was found to be highly uniform throughout the diode junction, effectively overcoming the main fabrication challenge in MIM diodes. The diodes exhibit strong non-linear current–voltage curves, have a typical zero-bias curvature coefficient of 5.4 V−1 and a zero-bias resistance of approximately 118 kΩ, a value considerably smaller than other MIM diode topologies and that allows more current to be rectified. Other results including current ratio and yield of the diode also competes favorably with the state-of-the-art MIM diodes such as the recently produced metal-octadecyltrichlorosilane (OTS)-metal structure.

Oxides for Rectenna Technology.

The quest to harvest untapped renewable infrared energy sources has led to significant research effort in design, fabrication and optimization of a self-biased rectenna that can operate without external bias voltage. At the heart of its design is the engineering of a high-frequency rectifier that can convert terahertz and infrared alternating current (AC) signals to usable direct current (DC). The Metal Insulator Metal (MIM) diode has been considered as one of the ideal candidates for the rectenna system. Its unparalleled ability to have a high response time is due to the fast, femtosecond tunneling process that governs current transport. This paper presents an overview of single, double and triple insulator MIM diodes that have been fabricated so far, in particular focusing on reviewing key figures of merit, such as zero-bias responsivity (β0), zero-bias dynamic resistance (R0) and asymmetry. The two major oxide contenders for MInM diodes have been NiO and Al2O3, in combination with HfO2, Ta2O5, Nb2O5, ZnO and TiO2. The latter oxide has also been used in combination with Co3O4 and TiOx. The most advanced rectennas based on MI2M diodes have shown that optimal (β0 and R0) can be achieved by carefully tailoring fabrication processes to control oxide stoichiometry and thicknesses to sub-nanometer accuracy.

A simulation study of multi-junction insulator tunnel diode for solar energy harvesting applications

There has been an ongoing demand of clean and inexpensive energy source for the sustainable growth of humanity. However, depletion of fossil fuels and fluctuation in oil prices have resulted in a global crisis for increasing the demand of clean and green energy. The world total energy consumption is currently higher than 55,235 TWh, and it grows at a rate of 2.5% annually. The increase in energy demand and decrease in energy supply signifies the urgent need to limit the dependency on fossil fuels and seek renewable sources of energy. The scientific communities and researchers are seeking alternative sources of renewable energy. Infrared (IR) energy harvesting is a promising contribution to sustainable energy demand. There is abundant IR energy available in the environment in the spectrum range from 2 to 11 μm (in wavelength), having maximum intensity at 10.6 μm (28.3 THz). The idea is to treat the waste heat as very high oscillating electromagnetic waves, which can be grabbed by a nanoantenna and further rectified by a diode into useful energy. This combination of nanoantenna and diode is known as ‘Rectenna system.’ Multilayer insulator diodes, which operate on the principle of electron tunneling, are one of the few candidates for such high-frequency operation. In this article, different combinations of the metal–insulator–insulator–metal (MII1I2M2) diode are studied for operation at high frequency (28.3 THz or 10.6 μm). The thickness of varying insulator layers with different dielectric constants is simulated and optimized to have the best resistor–capacitor time constant matching and an enhanced rectification. To the best of our knowledge, this is the first comprehensive and systematic study of the MII1I2M2 diode-based rectenna system for energy harvesting applications at 28.3 THz.

CVD-Grown Monolayer Graphene-Based Geometric Diode for THz Rectennas.

For THz rectennas, ultra-fast diodes are required. While the metal–insulator–metal (MIM) diode has been investigated in recent years, it suffers from large resistance and capacitance, as well as a low cut-off frequency. Alternatively, a geometric diode can be used, which is more suitable due to its planar structure. However, there is only one report of a THz geometric diode based on a monolayer graphene. It is based on exfoliated graphene, and thus, it is not suitable for mass production. In this work, we demonstrate chemical vapor deposition (CVD)-grown monolayer graphene based geometric diodes, which are mass-producible. The diode’s performance has been studied experimentally by varying the neck widths from 250–50 nm, the latter being the smallest reported neck width for a graphene geometric diode. It was observed that by decreasing the neck widths, the diode parameters such as asymmetry, nonlinearity, zero-bias resistance, and responsivity increased within the range studied. For the 50 nm neck width diode, the asymmetry ratio was 1.40 for an applied voltage ranging from −2 V to 2 V, and the zero-bias responsivity was 0.0628 A/W. The performance of the diode was also verified through particle-in-cell Monte Carlo simulations, which showed that the simulated current-voltage characteristics were consistent with our experimental results.

Aluminum scandium nitride-based metal–ferroelectric–metal diode memory devices with high on/off ratios

In this Letter, we report a back-end-of-line (BEOL), complementary metal–oxide–semiconductor (CMOS)-compatible Al0.64Sc0.36N-based ferroelectric diode that shows polarization-dependent hysteresis in its leakage currents. Our device comprises a metal/insulator/ferroelectric/metal structure (Pt/native oxide/Al0.64Sc0.36N/Pt) that is compatible with BEOL temperatures (≤ 350 °C) grown on top of a 4-in. silicon wafer. The device shows self-selective behavior as a diode with > 105 rectification ratio (for 5 V). It can suppress sneak currents without the need for additional access transistors or selectors. Furthermore, given the polarization-dependent leakage, the diode current–voltage sweeps are analogous to that of a memristor with an on/off ratio of ∼ 50 000 between low and high resistance states. Our devices also exhibit stable programed resistance states during DC cycling and a retention time longer than 1000 s at 300 K. These results demonstrate that this system has significant potential as a future high-performance post-CMOS compatible nonvolatile memory technology.

Calibration of a versatile multi-energy soft x-ray diagnostic for WEST long pulse plasmas.

A compact multi-energy soft x-ray diagnostic is being installed on the W Environment in Steady-state Tokamak (WEST), which was designed and built to test ITER-like tungsten plasma facing components in a long pulse (∼1000 s) scenario. The diagnostic consists of a pinhole camera fielded with the PILATUS3 photon-counting Si-based detector (≲100 kpixel). The detector has sensitivity in the range 1.6-30 keV and enables energy discrimination, providing a higher energy resolution than conventional systems with metal foils and diodes with adequate space and time resolution (≲1 cm and 2 ms). The lower-absorption cut-off energy is set independently on each one of the ∼100 kpixels, providing a unique opportunity to measure simultaneously the plasma emissivity in multiple energy ranges and deduce a variety of plasma parameters (e.g., Te, nZ, and ΔZeff). The energy dependence of each pixel is calibrated here over the range 3-22keV. The detector is exposed to a variety of monochromatic sources-fluorescence emission from metallic targets-and for each pixel, the lower energy threshold is scanned to calibrate the energy dependence. The data are fit to a responsivity curve ("S-curve") that determines the mapping between the possible detector settings and the energy response for each pixel. Here, the calibration is performed for three energy ranges: low (2.3-6 keV), medium (4.5-13.5 keV), and high (5.4-21 keV). We determine the achievable energy resolutions for the low, medium, and high energy ranges as 330eV, 640eV, and 950 eV, respectively. The main limitation for the energy resolution is found to be the finite width of the S-curve.

Graphene in 2D/3D Heterostructure Diodes for High Performance Electronics and Optoelectronics

AbstractDiodes made of heterostructures of the 2D material graphene and conventional 3D materials are reviewed in this manuscript. Several applications in high frequency electronics and optoelectronics are highlighted. In particular, advantages of metal–insulator–graphene (MIG) diodes over conventional metal–insulator–metal diodes are discussed with respect to relevant figures‐of‐merit. The MIG concept is extended to 1D diodes. Several experimentally implemented radio frequency circuit applications with MIG diodes as active elements are presented. Furthermore, graphene‐silicon Schottky diodes as well as MIG diodes are reviewed in terms of their potential for photodetection. Here, graphene‐based diodes have the potential to outperform conventional photodetectors in several key figures‐of‐merit, such as overall responsivity or dark current levels. Obviously, advantages in some areas may come at the cost of disadvantages in others, so that 2D/3D diodes need to be tailored in application‐specific ways.

Design and optimization of a nano-antenna hybrid structure for solar energy harvesting application

A novel hybrid structure with high responsivity and efficiency is proposed based on an L-shaped frame nano-antenna (LSFNA) array for solar energy harvesting application. So, two types of LSFNAs are designed and optimized to enhance the harvesting characteristics of traditional simple electric dipole nano-antenna (SEDNA). The LSFNA geometrical dimensions are optimized to have the best values for the required input impedance at three resonance wavelengths of λ res = 10 μm, 15 μm, and 20 μm. Then the LSFNAs with three different sizes are modeled like a planar spiral-shaped array (PSSA). Also, a fractal bowtie nano-antenna is connected with the PSSA in the array gap. This proposed hybrid structure consists of two main elements: (I) Three different sizes of the LSFNAs with two different material types are designed based on the thin-film metal–insulator–metal diodes that are a proper method for infrared energy harvesting. (II) The PSSA gap is designed based on the electron field emission proposed by the Fowler–Nordheim theory for the array rectification. Finally, the proposed device is analyzed. The results show that the PSSA not only has an averaged 3-time enhancement in the harvesting characteristics (such as return loss, harvesting efficiency, etc.) than the previously proposed structures but also is a multi-resonance wide-band device. Furthermore, the proposed antenna takes up less space in the electronic circuit and has an easy implementation process.

Nonstoichiometric Nanolayered Ni/NiO/Al2O3/CrAu Metal–Insulator–Metal Infrared Rectenna

Metal–insulator–metal (MIM) diodes with a high cutoff frequency are needed for efficient infrared rectification in optical rectenna systems. Such diodes require low resistance, low capacitance, and...

Tunneling diodes based on polymer infiltrated vertically aligned carbon nanotube forests

We report the fabrication and characterization of metal–insulator–metal diodes incorporating vertically aligned carbon nanotube (VACNT) arrays encased in polymer for applications in high frequency optoelectronics. Polydimethylsiloxane (PDMS) and epoxy infiltrating media are used in this study. VACNT forests are embedded with polymer to form a planarized surface over which an array of tunneling diodes is fabricated. Diodes comprising Al2O3 and HfO2 dielectric multilayers achieve highly nonlinear and asymmetric current-voltage characteristics. Results show that asymmetry in excess of 92 can be achieved with multi-insulator barrier tuning, though there is a strong correlation between asymmetry, resistance, and device longevity. With our best performing and most stable device structure (PDMS–VACNT/Al2O3-HfO2-Al2O3-HfO2/PEDOT:PSS), we provide a demonstration of optical-to-d.c. rectification at 638 nm, realizing a current responsivity of 0.65 µA W−1. Our approach to fabricating these VACNT diode arrays is facile and highly scalable. It is capable of being integrated with solution-processed materials and soft lithography techniques to create flexible devices for optical and infrared detection.

Metal Insulator Metal Diode: A Potential Candidate for Energy Harvesting Applications.

Metal-Insulator-Metal (MIM) diodes used for infrared detection and frequency mixing since many decades and their development for energy harvesting applications in rectenna solar cell has accelerated a decade ago. In the horizon of these applications less complex fabrication methodology, accurate simulation methods and optimum material combination are required. Ultra-fast response of MIM diodes makes them a potential candidate for solar energy harvesting applications. Here in this work, the design and fabrication issues of MIM diode from simulation methodology based on insulating thickness properties to the fabrication methodology are discussed. MIM diode for Al-Al₂O₃-Ag combination is fabricated and characteristics such as I(V), asymmetry and non-linearity are reported.