Nanoampere Range Research Articles

Facile formation of van der Waals metal contact with III-nitride semiconductors

Metal–semiconductor contacts play a pivotal role in controlling carrier transport in the fabrication of modern electronic devices. The exploration of van der Waals (vdW) metal contacts in semiconductor devices can potentially mitigate Fermi-level pinning at the metal–semiconductor interface, with particular success in two-dimensional layered semiconductors, triggering unprecedented electrical and optical characteristics. In this work, for the first time, we report the direct integration of vdW metal contacts with bulk wide bandgap gallium nitride (GaN) by employing a dry transfer technique. High-angle annular dark-field scanning transmission electron microscopy explicitly illustrates the existence of a vdW gap between the metal electrode and GaN. Strikingly, compared with devices fabricated with electron beam-evaporated metal contacts, the vdW contact device exhibits a responsivity two orders of magnitude higher with a significantly suppressed dark current in the nanoampere range. Furthermore, by leveraging the high responsivity and persistent photoconductivity obtained from vdW contact devices, we demonstrate imaging, wireless optical communication, and neuromorphic computing functionality. The integration of vdW contacts with bulk semiconductors offers a promising architecture to overcome device fabrication challenges, forming nearly ideal metal–semiconductor contacts for future integrated electronics and optoelectronics.

First-principle study of CrO2-BNNT-CrO2 based MTJ device using EHTB model and its application in a MRAM circuit

In this work we investigated the performance of Single-Walled Boron Nitride Nanotube (SWBNNT) sandwiched between CrO2 based Magnetic Tunnel Junction (MTJ) structures with atomistic simulations. MTJ based device-level simulation was performed using the Extended Huckel based Tight Binding (EHTB) model. The SWBNNT as a dielectric layer and CrO2 as Ferromagnetic (FM) layers based Magnetic Tunnel Junction (MTJ) heterostructure was computed. The proposed MTJ device operates at the nano-Ampere (nA) range depicting its potential application in a low-powered nanoelectronics device. It also shows a promising Tunnel Magnetoresistance (TMR) effect. The practical circuit-level implementation of the proposed MTJ device in Magnetic Random-Access Memory (MRAM) was validated using LTspice. Hence, the calculated static power consumption and writing energy per bit was minimal for S1 and S2 based MRAM circuit. The perfect switching operation was depicted by the proposed MTJ device based MRAM.

Composite channel 100 nm InP HEMT with ultrathin barrier for millimetre wave applications

This study introduces a High Electron Mobility Transistor (HEMT) designed for millimeter-wave applications, utilizing a composite channel structure based on InP and InGaAs-InAs-InGaAs. The proposed device incorporates an ultra-thin 2 nm barsrier layer, a distinctive composite channel topology, and a judicious selection of III-V materials. These features collectively contribute to an improved confinement of electrons within the channel, thereby improving the concentration of two-dimensional electron gas (2DEG), and consequently, enhancing the mobility and speed of the device. The proposed device exhibits a unity current gain frequency (f T) of 249 GHz and a maximum oscillation frequency (f MAX) of 523.9 GHz, accompanied by a current gain of 67.7 dB at 0.1 GHz. The off-state leakage current is maintained within the nanoampere range, and the minimum noise figure (NF MIN) is merely 0.76 dB at 10 GHz. A comparative analysis of DC and RF performance, along with an examination of associated parasitic elements, is conducted among various composite channel HEMTs proposed in recent literature. A quantitative justification is provided for the superiority of InGaAs-InAs-InGaAs channel HEMTs, establishing their heightened f T and f MAX. The proposed InGaAs-InAs-InGaAs channel HEMTs exhibit 1.4 times improved f T and f MAX, coupled with only half the NF MIN in comparison to their InGaAs-InP-InGaAs channel counterparts. To further comprehend the device’s behavior under varying RF conditions, a frequency-dependent intrinsic Field-Effect Transistor (FET) model is presented. This model facilitates the analysis of the device’s performance and allows the identification of the impact of individual parameters on the overall system.

A low-kiloelectronvolt focused ion beam strategy for processing low-thermal-conductance materials with nanoampere currents.

Ion beam-induced heat damage in thermally low conductive specimens such as biological samples is gaining increased interest within the scientific community. This is partly due to the increased use of FIB-SEMs in biology as well as the development of complex materials, such as polymers, which need to be analyzed. The work presented here looks at the physics behind the ion beam-sample interactions and the effect of the incident ion energy (set by the acceleration voltage) on inducing increases in sample temperature and potential heat damage in thermally low conductive materials such as polymers and biological samples. The ion beam-induced heat for different ion beam currents at low acceleration voltages is calculated using Fourier's law of heat transfer, finite element simulations, and numerical modelling results and compared to experiments. The results indicate that with lower accelerator voltages, higher ion beam currents in the nanoampere range can be used to pattern or image soft material and non-resin-embedded biological samples with increased milling speed but reduced heat damage.

Universality and Multiplication of Gigahertz-Operated Silicon Pumps with Parts Per Million-Level Uncertainty.

The universality of physical phenomena is a pivotal concept underlying quantum standards. In this context, the realization of a quantum current standard using silicon single-electron pumps necessitates the verification of the equivalence across multiple devices. Herein, we experimentally investigate the universality of pumped currents from two different silicon single-electron devices which are placed inside the cryogen-free dilution refrigerator whose temperature (mixing chamber plate) was ∼150 mK under the operation of the pump devices. By direct comparison using an ultrastable current amplifier as a galvanometer, we confirm that two pumped currents are consistent with ∼1 ppm uncertainty. Furthermore, we realize quantum-current multiplication with a similar uncertainty by adding the currents of two different gigahertz (GHz)-operated silicon pumps, whose generated currents are confirmed to be identical. These results pave the way for realizing a quantum current standard in the nanoampere range and a quantum metrology triangle experiment using silicon pump devices.

Proposed wide dynamic-range controllable current sources

Generating ultra-low currents using resistors is impractical especially in integrated circuits due to the wasting of much area associated with the required very large resistors. In this paper, three ultra-low current sources that are suitable for biomedical and implantable applications are proposed. The generated currents are in the nanoampere range. One of the proposed current sources depends on a modification of the conventional Widlar MOS current source in which a tunable subthreshold-region operated transistor is utilized as a controlled resistance. The proposed current source is suitable for low-voltage and low-power applications. Also, two digitally controlled current sources (DCCSs) are proposed. The DCCSs find a wide variety of applications in digital-to-analog converters, implantable microstimulators, and charge pumps. The three proposed current sources are analyzed quantitatively. They are also verified by simulation adopting the 45 nm CMOS Predictive Technology Model (PTM) with a power-supply voltage, VDD, equal to 1 V.

Ultrasonically sprayed Cs3Bi2I9 thin film based self-powered photodetector

In the present work, we report lead-free, all-inorganic, Cs3Bi2I9 perovskite-inspired films developed by ultrasonic spray deposition technique at various substrate temperatures which demonstrate promising photodetection properties without any external bias or power consumption. Uniform films of excellent adhesion to the substrate deposited from 150 to 400 °C were analyzed in detail using structural, morphological, optical and electrical characterization techniques. Highly crystalline films with well-packed grains were readily obtained below 325 °C substrate temperature. In addition, the degradation of the films during the growth at higher substrate temperatures was different from the normal decomposition of Cs3Bi2I9 due to post-deposition treatments. The thin films showed direct band gaps in the range of 1.8–2.1 eV with absorption coefficients in the order of ∼104 cm−1. Photocurrent in the nanoampere range was observed in all the phase-pure films under illumination by a 50 W halogen lamp. Moreover, the thin films were chemically stable even after rapid thermal processing up to 500 °C. Furthermore, self-powered photodetection using Ag/FTO/Cs3Bi2I9/C-Ag heterostructure is demonstrated under AM1.5 radiation as well as 532 and 405 nm laser illuminations. The highest responsivity and detectivity obtained for the Cs3Bi2I9-based photodetector were 0.0051 mAW−1 and 5.93 × 108 Jones (405 nm, 50 mW), respectively. Our investigations suggest that the spray deposited Cs3Bi2I9 films are promising for self-powered devices, especially in blue light detectors.

A 0.5-V Multiple-Input Bulk-Driven OTA in 0.18-μm CMOS

This article presents the experimental results for a multiple-input operational transconductance amplifier (MI-OTA). To achieve extended linearity under 0.5-V low voltage supply, the circuit employs three linearization techniques: the bulk-driven (BD), the source degeneration, and the input voltage attenuation created by the MI metal-oxide-semiconductor transistor technique (MI-MOST). Although the linearization techniques result in reduced dc gain, the self-cascode transistors are used to boost the gain of the MI-OTA. Furthermore, the MI-MOST simplifies the internal structure of the OTA and may reduce the complexity of the applications. The MI-OTA operates in the subthreshold region and offers tunability by a bias current in the nanoampere range. The circuit is capable to work with 0.5-V supply voltage while consuming 24.77 nW. The circuit was fabricated using the 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> Taiwan Semiconductor Manufacturing Company (TSMC) CMOS technology and it occupies a 0.01153-mm2 silicon area. Intensive simulation and experimental results confirm the benefits and robustness of the design.

Photo-thermionic emission and photocurrent dynamics in low crystallinity carbon nanotubes

Within this work, it is studied the photo-thermionic and photocurrent behavior of two kinds of carbon nanotube arrays, grown by chemical vapor deposition. One kind is fabricated by using a co-catalyst bilayer approach and other by a catalyst-free route by using a porous alumina membrane as a template. The carbon nanotubes fabricated by both approaches exhibit low crystallinity. To compute the thermal properties of the nanomaterials, a photothermal experiment was measured at 1064 nm wavelength, and numerical simulations were conducted to analyze the photo-thermionic emission dynamics. The high absorbance of the carbon nanotubes leads to reach temperatures above 1500 K, with time response in the millisecond order and emission currents in the nanoampere range. On the other hand, the photodetector behavior was confirmed by a single pulse experiment that induces fast photocurrent recognition associated to a photodiode. Our results highlighted the coexistence of stable states related to high-power and high-speed electronic conversion energy dependent on the growth mechanism of carbon nanotubes.

On the DC Offset Current Generated during Biphasic Stimulation: Experimental Study

This paper deals with the DC offset currents generated by a platinum electrode matrix during biphasic stimulation. A fully automated test bench evaluates the nanoampere range DC offset currents in a realistic and comprehensive scenario by using platinum electrodes in a saline solution as a load for the stimulator. Measurements are performed on different stimulation patterns for single or dual hexagonal stimulation sites operating simultaneously and alternately. The effectiveness of the return electrode presence in reducing the DC offset current is considered. Experimental results show how for a defined nominal injected charge, the generated DC offset currents differ depending on the stimulation patterns, frequency, current amplitude, and pulse width of a biphasic signal.

A Low-Power CMOS Current Reference for Piezoelectric Energy Harvesters

This article proposes a nanoscale complementary metal-oxide-semiconductor (CMOS) current reference design for low power analog and digital devices. A self-biased circuit is developed within the current reference. The current reference can compensate for temperature changes and voltage fluctuations. Simulation results showed a low current around 12 nA. The design is capable of working in a broad range of power supply voltages. In the interface with 0.35 μm fabrication process, a bias voltage is generated with currents in the nanoampere range. The present current reference is qualified to be used in digital-analog circuits, such as operational amplifiers or oscillators, and is designed to be suitable for energy harvesting interfaces, because of the high efficiency and low power consumption.

Ultrasensitive Photoresponse of Graphene Quantum Dots in the Coulomb Blockade Regime to THz Radiation.

Graphene quantum dots (GQDs) have recently attracted considerable attention, with appealing properties for terahertz (THz) technology. This includes the demonstration of large thermal bolometric effects in GQDs when illuminated by THz radiation. However, the interaction of THz photons with GQDs in the Coulomb blockade regime, i.e., single electron transport regime, remains unexplored. Here, we demonstrate the ultrasensitive photoresponse to THz radiation (from <0.1 to 10 THz) of a hBN-encapsulated GQD in the Coulomb blockade regime at low temperature (170 mK). We show that THz radiation of ∼10 pW provides a photocurrent response in the nanoampere range, resulting from a renormalization of the chemical potential of the GQD of ∼0.15 meV. We attribute this photoresponse to an interfacial photogating effect. Furthermore, our analysis reveals the absence of thermal effects, opening new directions in the study of coherent quantum effects at THz frequencies in GQDs.

Design 5.0 µm Gap Aluminium Interdigitated Electrode for Sensitive pH Detection

The aim of the research study to design high sensitive biosensor for medical applications. IDE pattern was designed using AutoCAD software with 5 µm ginger gap. The fabrication process was done using a conventional photolithography process and standard CMOS process. The fabricated electrode was physically characterized using a low power microscope (LPM) and a high power microscope (HPM). The electrically validated through I-V measurements and chemically tested with different pH buffer solutions. Al IDE was well fabricated with 0.1 µm tolerance between the design mask and fabricated IDEs. Electrical measurements confirmed that IDE was well fabricated without any shortage and results of similar IDE samples were confirmed that the repeatability of the device. The extremely small current variations in nano ampere range were quantitatively detected using an extra small volume of 2 µl for different pH buffer solutions. It is confirmed that IDEs are sensitive in both alkali and hydroxyl ions medium.

Motility enhancement of human spermatozoa using electrical stimulation in the nano-Ampere range with enzymatic biofuel cells.

Sperm motility is a crucial factor for normal fertilisation that is partly supported by mitochondrial activity. Enzymatic biofuel cells (EBFCs) generate electric currents by an electron grade from anodic to cathodic electrodes in a culture media. We demonstrate that electrical stimulation by EBFC at the nano-Ampere range enhances sperm motility that can potentially allow the development of a new therapeutic tool for male infertility, including poor motility. EBFC was set up with three different electrical currents (112 nA/cm2 and 250 nA/cm2) at two different times (1 h, 2 h). Each sample was evaluated for its motility by computer-assisted sperm analyses and sperm viability testing. In the expanded study, we used the optimal electrical current of the EBFC system to treat asthenozoospermia and sperm with 0% motility. Results showed that optimal electrical stimulation schemes with EBFCs enhanced sperm motility by 30–40% compared with controls. Activated spermatozoa led to tyrosine phosphorylation in the tail area of the sperm following the electrical stimulation in the nano-Ampere range. However, the electrically stimulated group did not exhibit increased acrosomal reaction rates compared with the control group. In cases related to asthenozoospermia, 40% of motility was recovered following the electrical stimulation at the nano-Ampere range. However, motility is not recovered in sperm with 0% motility. In conclusion, we found that sperm motility was enhanced by exposure to electrical currents in the nano-Ampere range induced by optimal EBFCs. Electrical stimulation enhanced the motility of the sperm though tyrosine phosphorylation in spermatozoa. Therefore, our results show that electrical currents in the nano-Ampere range can be potentially applied to male infertility therapy as enhancers of sperm motility in assisted reproductive technology.

Graphene/fluorographene heterostructure for nano ribbon transistor channel

4H-SiC multilayer graphene/fluorographene heterostructures have been implemented to fabricate a 40 nm transistor channel. The plasma-assisted fluorination process with a carbon-to-fluorine ratio of ∼1 allows the passivation of the sidewalls with a substantial reduction in the channel width to form multilayer graphene nanoribbons (GNRs). A graphene channel is completely embedded in the passivated top and sidewalls of graphene. the gate leakage is in the nanoampere range, which makes the fluorinated dielectric robust enough for tunnel barrier. We have fabricated top gate transistors using this heterostructure and demonstrated the onset of rectification using this process. Despite the limited on/off ratio, I–V characteristics of GNRs of 40 nm channel width show a clear improvement compared to 50 μm device indicating that this process is a potential route to pattern nanoribbons.

A 10-mA LDO With 16-nA IQ and Operating From 800-mV Supply

A low-dropout (LDO) regulator with a quiescent current in the tens of nanoampere range and operating from 800-mV supply is proposed. A rail-to-rail buffer with zero input–output (I/O) voltage shift and based on the differential flipped voltage follower is used for combined gate and bulk driving of the output device. Therefore, bulk modulation with forward body bias is implemented without any additional amplifier. The proposed buffer is a crucial block for the sub-1-V supply and for limiting the contribution of the output device to the quiescent current. The error amplifier (EA) is adaptively biased with a bias shaper block, which implements a current limiting at high loads and a linear dependence on the output current at moderate loads. The feedback signal for the bias control is the output of the amplifier instead of the gate voltage of the pass device, thus combining a nanoampere bias at light load with the ability to follow a fast output current transient. Finally, a corner-tracking load is used to set the bias current of the output device to the minimum value at the target stability margin over the temperature and process parameters’ space. The LDO was implemented in a 55-nm CMOS technology. The measured quiescent current is 16 nA with a minimum power supply rejection of 42.7 dB up to 50 kHz and a maximum load current of 10 mA. In order to compare the transient behavior of the state-of-the-art designs, a modified figure of merit is proposed, taking into account the penalty caused by the low supply.

Fermi level-tuned optics of graphene for attocoulomb-scale quantification of electron transfer at single gold nanoparticles

Measurement of electron transfer at single-molecule level is normally restricted by the detection limit of faraday current, currently in a picoampere to nanoampere range. Here we demonstrate a unique graphene-based electrochemical microscopy technique to make an advance in the detection limit. The optical signal of electron transfer arises from the Fermi level-tuned Rayleigh scattering of graphene, which is further enhanced by immobilized gold nanostars. Owing to the specific response to surface charged carriers, graphene-based electrochemical microscopy enables an attoampere-scale detection limit of faraday current at multiple individual gold nanoelectrodes simultaneously. Using the graphene-based electrochemical microscopy, we show the capability to quantitatively measure the attocoulomb-scale electron transfer in cytochrome c adsorbed at a single nanoelectrode. We anticipate the graphene-based electrochemical microscopy to be a potential electrochemical tool for in situ study of biological electron transfer process in organelles, for example the mitochondrial electron transfer, in consideration of the anti-interference ability to chemicals and organisms.

Design of a low-current shunt-feedback transimpedance amplifier with inherent loop-stability

In this paper we propose a new architecture for enhancing the performance of a transimpedance amplifier used for low-currents, and in particular, that used in biosensing. It is usually the first block in biomedical acquisition systems for converting a current in the nanoampere and picoampere range into a proportional voltage, with an amplitude suitable for further processing. There exist two main amplifier topologies for achieving this, current-mode and shunt-feedback mode. This paper introduces a shunt-feedback amplifier that embodies current-mode operation and thereby offers the advantages of both existing schemes. A conventional shunt-feedback amplifier has a number of stages and requires compensation components to achieve stability of the feedback loop. The exemplary circuit described is inherently stable because a high gain is effectively achieved in one stage that has a dominant pole controlling the frequency response. Exhibiting complementary symmetry, the configuration has an input port that is very close to earth potential. This enables the configuration to handle bidirectional input signals such are as met with in electrochemical ampero-metric biosensors. For the 0.35 µm process adopted and ± 3.3 V rail supplies, the power dissipation is 330 µW. With a transimpedance gain of 120 dBΩ the incremental input and output resistances are less than 2 Ω and the − 3 dB bandwidth for non-optical input currents is 8.2 MHz. The input referred noise current is 3.5 pA/√Hz.

A nano-ampere current reference circuit in a 0.5 μm CDMOS technology

A low power current reference circuit with an enable-control terminal is presented in this work, which has been developed in 0.5 μm CDMOS technology. The circuit is capable of providing the reference current in a nano-ampere range for the supply voltage from 2 V to 3 V in the temperature range from −30 °C to 85 °C. The simulation and measurement results demonstrated that the reference current achieves the line regulation of 4.67%/V, the average temperature coefficient of 361.59 ppm/°C when simulations and measurements are carried out for 8 die-samples under the same supply-voltage and temperature variations. The complete designed circuit consumes approximately 765.1 nA current to generate about 90 nA reference current at 3 V power supply while occupying an area of 0.0217mm2.

A 352nW, 30 ppm/°C all MOS nano ampere current reference circuit

In this work, an ultra low power all-MOSFET based current reference circuit, developed in 0.18µm CMOS technology, is presented. The proposed circuit is based on the classical resistor-less beta multiplier circuit with an additional temperature compensation feature. The circuit is capable of providing the reference current in a nanoampere range for the supply voltage ranging from 1V to 2V in the industrial temperature range of −40°C to 85°C. The measurements were performed on 10 prototypes. The measured mean value of the reference current is 58.7nA with a mean temperature coefficient value of 30ppm/°C. In addition, the measured mean line regulation is 3.4%/V in the given supply voltage range. The total current consumption of the circuit is 352nA and the chip area is 0.036mm2.