Thin HfO2 Layers Research Articles

Interfacial passivation by using an amorphous hafnium oxide thin layer toward improved CH3NH3PbI3/Si heterojunction photodetectors

In this paper, we reported the fabrication of improved CH3NH3PbI3/Si heterojunction photodetectors (PDs) achieved by passivating the interfacial defects by a low-temperature atomic layer deposition-grown thin amorphous HfO2 layer. The results suggested that the HfO2 thin layer effectively passivated the surface defects of Si and slightly improved the qualities of CH3NH3PbI3 thin films in terms of increasing the grain sizes. Current–voltage measurements suggested that the HfO2 thin layer suppressed interfacial Shockley–Read–Hall recombination, which decreased the dark current and simultaneously increased the photocurrent. However, a thick HfO2 layer resulted in a decrease in the photocurrent because of the insulting nature of HfO2. A champion performance was obtained by employing a 5 nm HfO2 layer, where the responsivity and detectivity were 0.6 mA/W and 8.0 × 1010 Jones, respectively, which are two times and four times as high as those PDs without the HfO2 layer. The results will provide a simple strategy for improving the performance of perovskite/Si heterojunction PDs in the future.

Third and fifth order nonlinear susceptibilities in thin HfO2 layers.

Third harmonic generation (THG) from dielectric layers is investigated. By forming a thin gradient of HfO2 with continuously increasing thickness, we are able to study this process in detail. This technique allows us to elucidate the influence of the substrate and to quantify the layered materials third χ(3)(3ω: ω, ω, ω) and even fifth order χ(5)(3ω: ω, ω, ω, ω, - ω) nonlinear susceptibility at the fundamental wavelength of 1030 nm. This is to the best of our knowledge the first measurement of the fifth order nonlinear susceptibility in thin dielectric layers.

Alleviation of Self-Heating Effect in Top-Gated Ultrathin In2O3 FETs Using a Thermal Adhesion Layer

In this work, a thin layer of hexagonal boron nitride (h-BN) or HfO2 serves as an adhesion layer between the ultrathin atomic-layer-deposited (ALD) indium oxide (In2O3) channel and a sapphire substrate to enhance the thermal interfacial conductance. A thermo-reflectance (TR) measurement system with high spatial resolution is introduced to experimentally demonstrates the improvement. With the thin h-BN or HfO2 interlayer, the temperature elevation ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {T}$ </tex-math></inline-formula> ) induced by self-heating effect (SHE) is decreased by roughly 9% or 27%, respectively. To quantify the improvement of the interfacial heat transfer, a steady-state thermal diffusion model with a finite-element method is combined with the experimental TR observation to extract the effective thermal boundary conductance (TBC) values in each case. It is shown that the effective TBC is ameliorated by a factor of 2 or 7 with the h-BN or HfO2 interlayer, which is responsible for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta {T}$ </tex-math></inline-formula> reduction. Furthermore, phonon density of states (PDOS) distribution mismatch implies that the intersection over union (IOU) ratio in the acoustic phonon region of In2O3 with h-BN or HfO2 is roughly 3 or 11 times higher than that directly with sapphire, which is responsible for the profound TBC enhancement. Based on this, ultrahigh maximum drain current of 2.4 mA/ <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> is achieved with 2.1-nm-thick In2O3 channel on a sapphire substrate with an HfO2 interlayer in between due to the alleviated SHE.

Reliability of TCAD study for HfO2-doped Negative capacitance FinFET with different Material-Specific dopants

Attaining the ferroelectric (FE) polarization in a thin HfO2 layer using a specific dopant is a widely adopted way to realize Negative Capacitance (NC) FET. In a general TCAD simulation study of NC-based devices, the NC property of the FE layer is strongly dependent on the values of Landau parameters (α,β,γ,ρ,g), which are unique for specific dopants and FE thickness. In this paper, for the first time, we investigated the reliability of TCAD simulations with which NC FinFET is simulated for a specific dopants-based FE-HfO2 layer. The possible dopants used to realize a thin-HfO2 layer as a FE layer are Al, Gd, La, Si, Sr, Y, and Zr. Each dopant has different (α,β,γ,ρ,g) and thus offers a different NC regime of operation, i.e., S-curve. α and β are the dominant parameters if we consider the uniform polarization under quasi-static analysis. Further, the change in ambient temperature alters the value of α, resulting in changes in the NC-state. Hence, for the reliable TCAD-based NC study, the precise selection of Landau parameters and dopants is needed for optimized performances.

Ion Drift and Polarization in Thin SiO2 and HfO2 Layers Inserted in Silicon on Sapphire.

To reduce the built-in positive charge value at the silicon-on-sapphire (SOS) phase border obtained by bonding and a hydrogen transfer, thermal silicon oxide (SiO2) layers with a thickness of 50–310 nm and HfO2 layers with a thickness of 20 nm were inserted between silicon and sapphire by plasma-enhanced atomic layer deposition (PEALD). After high-temperature annealing at 1100 °C, these layers led to a hysteresis in the drain current–gate voltage curves and a field-induced switching of threshold voltage in the SOS pseudo-MOSFET. For the inserted SiO2 with a thickness of 310 nm, the transfer transistor characteristics measured in the temperature ranging from 25 to 300 °C demonstrated a triple increase in the hysteresis window with the increasing temperature. It was associated with the ion drift and the formation of electric dipoles at the silicon dioxide boundaries. A much slower increase in the window with temperature for the inserted HfO2 layer was explained by the dominant ferroelectric polarization switching in the inserted HfO2 layer. Thus, the experiments allowed for a separation of the effects of mobile ions and ferroelectric polarization on the observed transfer characteristics of hysteresis in structures of Si/HfO2/sapphire and Si/SiO2/sapphire.

Nanocrystallized Ge-Rich SiGe-HfO2 Highly Photosensitive in Short-Wave Infrared.

Group IV nanocrystals (NCs), in particular from the Si–Ge system, are of high interest for Si photonics applications. Ge-rich SiGe NCs embedded in nanocrystallized HfO2 were obtained by magnetron sputtering deposition followed by rapid thermal annealing at 600 °C for nanostructuring. The complex characterization of morphology and crystalline structure by X-ray diffraction, μ-Raman spectroscopy, and cross-section transmission electron microscopy evidenced the formation of Ge-rich SiGe NCs (3–7 nm diameter) in a matrix of nanocrystallized HfO2. For avoiding the fast diffusion of Ge, the layer containing SiGe NCs was cladded by very thin top and bottom pure HfO2 layers. Nanocrystallized HfO2 with tetragonal/orthorhombic structure was revealed beside the monoclinic phase in both buffer HfO2 and SiGe NCs–HfO2 layers. In the top part, the film is mainly crystallized in the monoclinic phase. High efficiency of the photocurrent was obtained in a broad spectral range of curves of 600–2000 nm at low temperatures. The high-quality SiGe NC/HfO2 matrix interface together with the strain induced in SiGe NCs by nanocrystallization of both HfO2 matrix and SiGe nanoparticles explain the unexpectedly extended photoelectric sensitivity in short-wave infrared up to about 2000 nm that is more than the sensitivity limit for Ge, in spite of the increase of bandgap by well-known quantum confinement effect in SiGe NCs.

Sensitivity optimization of a Double-Gated ISFET pH-sensor with HfO2/SiO2 gate dielectric stack

This paper investigates the sensitivity enhancement of Ion-Sensitive Field Effect Transistor (ISFET) pH-sensor using double-gate operation and illustrates how different structure modifications between the top and back oxides give different sensitivity gain factors. The gain factor is controlled through top and back oxide thickness, channel thickness and SiGe channel material. The sensitivity at the back gate is 59.52 mV/pH (27 °C) and the amplified sensitivity at the front gate reaches 476.54 ±33 mV/pH (27 °C). Furthermore, the issues related to high sensitivity-amplification such as sensitivity variation and dielectric breakdown are discussed, followed by optimization of the device structure in the linear regime to overcome them. Stacking a thin HfO2 layer over the top SiO2 layer helps in preventing dielectric breakdown at high sensitivity analysis. Synopsys TCAD is utilized for this proposed work with the electrolyte material and site-binding reactions being modeled through user-defined features of TCAD with explicit references from experimental data.

Performance of CsPbBr3/HfO2/Si: Performance‐Enhanced CsPbBr3/HfO2/Si Heterostructure Optoelectronics through the Tunneling Effect (Adv. Mater. Interfaces 11/2021)

The tunneling effect through a thin HfO2 layer enables a CsPbBr3/HfO2/Si heterostructure photodetector with enhanced optoelectronic performance. In article number 2100279, Yu Zhang and co-workers demonstrate that the optoelectronic performance of the CsPbBr3/HfO2/Si heterostructure device can be modulated through both Vds and Vgs, providing flexibility for different applications.

Performance‐Enhanced CsPbBr3/HfO2/Si Heterostructure Optoelectronics through the Tunneling Effect

AbstractCsPbBr3, as an all‐inorganic perovskite, has attracted considerable research interest due to its excellent optoelectronic properties. However, because the electronic properties of CsPbBr3 are not satisfactory, the relatively low on/off ratio and long photoresponse time of CsPbBr3 devices limit further applications. In this work, a CsPbBr3 device with high performance is successfully fabricated through a simple process using a CsPbBr3 colloid, and the photoresponse performance of the device is investigated under different external factors. By inserting a thin HfO2 layer, CsPbBr3‐based heterostructure devices exhibit much better performances, including an enhanced photocurrent of ≈10 µA, a responsivity of 45.05 A W−1, a detectivity of 9.12 × 1010 Jones, an external quantum efficiency of 12445%, and rise/fall times of 600 µs/300 µs, respectively. A physical mechanism is proposed to explain the photoresponse property promotion in CsPbBr3 devices, which can be attributed to the tunneling effect between CsPbBr3 and Si through the thin HfO2 layer. More importantly, the optoelectrical properties of the proposed CsPbBr3/HfO2/Si heterostructure device can be modulated through both Vds and Vgs. This work offers a valuable strategy and a practical scheme that can be generalized to other perovskite and heterostructure devices.

Fully Transparent Friction‐Modulation Haptic Device Based on Piezoelectric Thin Film

AbstractStanding Lamb waves in vibrating plates enable haptic interfaces. If the out‐of‐plane displacement of these waves exceeds 1 µm at frequencies above 25 kHz, a silent friction modulation can be created between a human finger and a vibrating plate. A fully transparent friction‐modulation haptic device based on a piezoelectric thin film is demonstrated. The antisymmetric Lamb mode induced at 73 kHz allows for a functional performance that fulfills all conditions for practical use. Out‐of‐plane displacement reaches 2.9 µm when 150 V unipolar voltage is applied. The average transmittance of the whole transducer reaches 75%. The key points of this technology are: 1) a thin HfO2 layer between lead zirconate titanate film and substrate that prevents chemical reaction between them; 2) the efficient integration of transparent indium tin oxide electrodes and solution‐derived piezoelectric lead zirconate titanate thin film onto optical‐grade fused silica; and 3) the use of a transparent insulating layer made of SU‐8 photoresist.

Ferroelectric memory field-effect transistors using CVD monolayer MoS2 as resistive switching channel

Ferroelectric field-effect transistors (FeFETs) have been considered as promising electrically switchable nonvolatile data storage elements due to their fast switching speed, programmable conductance, and high dynamic range for neuromorphic applications. Meanwhile, FeFETs can be aggressively shrunk to the atomic scale for a high density device integration, ideally, without comprising the performance by introducing two-dimensional (2D) materials. So far, the demonstrated 2D material-based FeFETs mainly rely on mechanically exfoliated flakes, which are not favorable for large-scale industrial applications, and FeFETs based on organic ferroelectrics typically show a large writing voltage (e.g., &amp;gt;±20 V), making these types of memory devices impractical to be commercially viable. Here, we demonstrate that monolayer MoS2 grown by chemical vapor deposition (CVD) can be used as a resistive switching channel to fabricate FeFETs, in which the MoS2 channel is modulated by a hybrid gate stack of HfO2/ferroelectric HfZrOx thin films. The programming processes in the 2D MoS2 FeFETs originate from the ferroelectric polarization switching, yielding two distinct write and erase states for data storage and cumulative channel conductance for artificial synapse applications. Our 2D FeFETs show a low-voltage-driven feature (&amp;lt;±3 V) and gate-tunable ferroelectric hysteresis characteristics. The thin HfO2 layer in the hybrid gate stack likely plays crucial roles in preserving the ferroelectricity of the device and lowering the threshold of switching voltages through energy redistribution. Our findings open an avenue for the use of CVD-grown layered materials as the resistive switching mediums combined with HfO2-based ferroelectrics for future energy-efficient “brain-on-a-chip” hardware.

High-temperature stable refractory nanoneedles with over 99% solar absorptance

Solar absorber coatings have widely been investigated for solar-thermal technologies including concentrated solar power and solar thermochemistry. While various nanostructures such as nanowires and nanotubes have been commonly used for high solar absorptance owing to their potent light trapping effect, the high temperature stability of these nanostructures has yet to be established due to either coarsening of nanostructures or oxidation of certain materials in air (e.g., Si and C). In this work, we developed a nanostructured solar absorber from a family of high-temperature refractory spinel oxides, Co3O4 and CuCo2O4, with ultra-high solar absorptance over 99%. Once coated with a thin layer of HfO2 or SiO2 through atomic layer deposition, the Co3O4 and CuCo2O4 nanoneedles preserve their high aspect ratio and sharp tips, allowing the solar absorbers to maintain the superior absorptivity and excellent thermal stability at an elevated temperature for an extended period (650 °C and 800 °C for 100 h for passivated Co3O4 and Cu1Co2O4, respectively). These results suggest that solar absorbers made from refractory spinel oxide nanoneedles can be used for high-temperature solar thermal applications with ultrahigh absorptance.

Wafer-scale HfO2 encapsulated silicon nanowire field effect transistor for efficient label-free DNA hybridization detection in dry environment

AbatractSilicon nanowire (SiNW) charge based biosensors are attractive for DNA sensing applications due to their compactness and large surface-to-volume ratio. Small feature size, low production cost, repeatability, high sensitivity and selectivity are some of the key requirements for biosensors. The most common e-beam manufacturing method employed to manufacture sub-nm SiNWs is both cost and time intensive. Therefore, we propose a highly reproducible CMOS industry grade low-cost process to fabricate SiNW-based field effect transistors on 4″-wafers. The 60 nm wide SiNWs reported in this paper are fabricated using the sidewall transfer lithography process which is a self-aligned-double-patterning I-line lithography process that also facilitates encapsulation of the SiNW surface with a thin HfO2 layer on which DNA probes are grafted to finalize the biosensors. Upon DNA hybridization, SiNW devices exhibit threshold voltage shift larger than the noise introduced by the exposition to saline solutions used for the bioprocesses. More specifically, based on a statistical analysis, we demonstrate that 85% of the tested devices exhibit a positive threshold voltage shift after DNA hybridization. These promising results make way for the monolithic integration of SiNW biosensors and CMOS circuitry to realize a point of care device which can offer reliable real time electrical readout.

Investigation of DC and RF Performance of Novel MOSHEMT on Silicon Substrate for Future Submillimetre Wave Applications

In this work, the DC and RF performance of a 20 nm gate length novel metal oxide semiconductor high electron mobility transistor (MOSHEMT) on Silicon substrate is studied using Sentaurus TCAD tool. The proposed MOSHEMT device features a novel T-gate structure, heavily doped In0.52Ga0.48As source/drain regions, delta doped planes on both sides of the In0.75Ga0.25As/InAs/In0.75Ga0.25As composite channel, a multi layer cap and a very thin layer of HfO2 as gate dielectric. The TCAD simulation results obtained at room temperature using hydrodynamic carrier transport model indicates that the 20 nm gate length proposed MOSHEMT device is capable of providing a peak drain current of 2450 mA/mm at VDS = 0.6 V and the peak transconductance obtained for the proposed device is 2900 mS/mm. The fT and fmax obtained for the Lg = 20 nm proposed MOSHEMT on Silicon substrate are 372 and 480 GHz respectively. At 300 K, the measured Hall mobility of the electrons in the quantum well channel is 9600 cm2/(V s). The on state resistance (RON) obtained for the Lg = 20 nm proposed device is 116 Ohm μm. These devices are undoubtedly, the most suitable candidates for future sub millimetre wave applications.

Depletion Mode MOSFET Using La-Doped BaSnO3 as a Channel Material.

The high room-temperature mobility that can be achieved in BaSnO3 has created significant excitement for its use as channel material in all-perovskite-based transistor devices such as ferroelectric field effect transistor (FET). Here, we report on the first demonstration of n-type depletion-mode FET using hybrid molecular beam epitaxy grown La-doped BaSnO3 as a channel material. The devices utilize a heterostructure metal-oxide semiconductor FET (MOSFET) design that includes an epitaxial SrTiO3 barrier layer capped with a thin layer of HfO2 used as a gate dielectric. A field-effect mobility of ∼70 cm2 V-1 s-1, a record high transconductance value of >2mS/mm at room temperature, and the on/off ratio exceeding 107 at 77 K were obtained. Using temperature- and frequency-dependent transport measurements, we quantify the impact of the conduction band offset at the BaSnO3/SrTiO3 interface as well as bulk and interface traps on device characteristics.

MoS2 Functionalization with a Sub-nm Thin SiO2 Layer for Atomic Layer Deposition of High-κ Dielectrics

Several applications of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) in nanoelectronic devices require the deposition of ultrathin pinhole free high-κ dielectric films on 2D TMDs. However, deposition of nm-thin high-κ dielectric films on 2D TMDs remains challenging due to the inert TMD surface. Here, we demonstrate that the surface of a synthetic polycrystalline 2D MoS2 film is functionalized with SiO2 to enable the atomic layer deposition (ALD) of thin and continuous Al2O3 and HfO2 layers. The origins of nucleation, the growth mode, and layer coalescence process have been investigated by complementary physical characterization techniques, which can determine the chemical bonds, absolute amount, and surface coverage of the deposited material. SiO2 is prepared by oxidizing physical vapor deposited Si in air. The surface hydrophilicity of MoS2 significantly increases after SiO2 functionalization owing to the presence of surface hydroxyl groups. SiO2 layers with a Si content of...

20 nm high performance novel MOSHEMT on InP substrate for future high speed low power applications

In this work, the DC and RF performance of a 20 nm gate length novel metal oxide semiconductor high electron mobility transistor (MOSHEMT) on InP substrate is studied using Sentaurus TCAD tool. The proposed MOSHEMT device features heavily doped In0.52Ga0.48As source/drain regions, delta doped planes on both sides of the In0.7Ga0.3As/InAs/In0.7Ga0.3As composite channel, a multi layer cap and a very thin layer of HfO2 as gate dielectric. The TCAD simulation results obtained at room temperature using physics based carrier transport model indicates that the 20 nm gate length proposed MOSHEMT device is capable of providing a peak drain current of 2860 mA/mm at VDS = 0.6 V and the peak transconductance obtained for the proposed device is 2890 mS/mm. The fT and fmax obtained for the Lg = 20 nm proposed MOSHEMT on InP substrate are 537 GHz and 631 GHz respectively. At 300 K, the measured Hall mobility of the electrons in the quantum well channel is 11620 cm2/V. The on state resistance (RON), subthreshold swing (SS) and drain induced barrier lowering (DIBL) obtained for the Lg = 20 nm proposed InP-MOSHEMT are 105 Ω μm, 160 mV/dec and 178 mV/V respectively. These devices are undoubtedly, the most suitable candidates for future high speed, low power post silicon logic applications.

Atomic layer deposition of SnO2 on MXene for Li-ion battery anodes

In this report, we show that oxide battery anodes can be grown on two-dimensional titanium carbide sheets (MXenes) by atomic layer deposition. Using this approach, we have fabricated a composite SnO2/MXene anode for Li-ion battery applications. The SnO2/MXene anode exploits the high Li-ion capacity offered by SnO2, while maintaining the structural and mechanical integrity of the conductive MXene platform. The atomic layer deposition (ALD) conditions used to deposit SnO2 on MXene terminated with oxygen, fluorine, and hydroxyl-groups were found to be critical for preventing MXene degradation during ALD. We demonstrate that SnO2/MXene electrodes exhibit excellent electrochemical performance as Li-ion battery anodes, where conductive MXene sheets act to buffer the volume changes associated with lithiation and delithiation of SnO2. The cyclic performance of the anodes is further improved by depositing a very thin passivation layer of HfO2, in the same ALD reactor, on the SnO2/MXene anode. This is shown by high-resolution transmission electron microscopy to also improve the structural integrity of the SnO2/MXene anode during cycling. The HfO2 coated SnO2/MXene electrodes demonstrate a stable specific capacity of 843 mAh/g when used as Li-ion battery anodes.

Fabrication of InGaN thin-film transistors using pulsed sputtering deposition.

We report the first demonstration of operational InGaN-based thin-film transistors (TFTs) on glass substrates. The key to our success was coating the glass substrate with a thin amorphous layer of HfO2, which enabled a highly c-axis-oriented growth of InGaN films using pulsed sputtering deposition. The electrical characteristics of the thin films were controlled easily by varying their In content. The optimized InGaN-TFTs exhibited a high on/off ratio of ~108, a field-effect mobility of ~22 cm2 V−1 s−1, and a maximum current density of ~30 mA/mm. These results lay the foundation for developing high-performance electronic devices on glass substrates using group III nitride semiconductors.

Observation of Thermal Beaming from Tungsten and Molybdenum Bull’s Eyes

Although losses in plasmonic films can be detrimental for optoelectronics, they can be exploited to create novel thermal emitters. Surface plasmon polaritons that are thermally excited on a heated metal surface can be converted to photons with useful properties. We demonstrate highly tailored thermal emission from tungsten and molybdenum films patterned with a series of circular concentric grooves (i.e., a bull’s eye). At 900 °C our structures emit an infrared beam normal to the film that is spectrally narrow (tens of nanometers) and highly directional (∼2° angular divergence). The peak wavelength (3.5 μm) can be tuned with groove periodicity. To enhance the thermal stability of the structures, we add a thin layer of HfO2. Such devices, with their simple design and low thermal mass, provide interesting incandescent light sources for various applications.