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Microelectrodes are used in a wide range of applications from analytical electrochemistry and biomolecular sensing to in vivo implants. While a variety of insulating materials have been used to define the microelectrode active area, most are not suitable for nanoscale electrodes (

Recent advances in the field of two-dimensional (2D) transition metal dichalcogenide (TMD) materials have indicated that atomic layer deposition (ALD) of the metal oxide and subsequent sulfidation could offer a method for the synthesis of large area two-dimensional materials such as MoS2 with excellent layer control over the entire substrate. However, growing large area oxide films by ALD with sub 1 nm nucleation coalescence remains a significant challenge, and the necessary steps are unexplored. In this work, we demonstrate the necessary process improvements required to achieve sub 1 nm nucleation control by characterization of nucleation domains formed by oxide deposition. Synthesis of the TMD MoS2 from sulfidation of oxide deposited by both thermal ALD from (tBuN)2(NMe2)2Mo and O3 and plasma enhanced ALD (PEALD) from (tBuN)2(NMe2)2Mo and remote O2 plasma was performed. Large uniform MoS2 areas were achieved by optimizing the effects of various growth process conditions and surface treatments on the ALD...

Plasma-enhanced atomic layer deposition (PEALD) of ultrathin (∼7 nm) slightly Ti-rich Ba x Ti y O z (BTO) films with different Al-doping concentration ([Al]/([Al] + [Ba] + [Ti]) = 0 to 22 at%) was studied. In particular, the effects of Al-doping in BTO on compositional, crystallographic and electrical properties were investigated. Previously, BTO films with a Ti cation composition, [Ti]/([Ba] + [Ti]) = ∼60 at% was reported to be advantageous for crystallization, resulting in superior dielectric properties. These Ti-rich BTO films, however, suffered from high leakage currents, necessitating the change in its crystalline structure as well as elemental composition. By incorporating Al 2 O 3 into the BTO films, the leakage current can be controlled, where the BTO films with an Al-doping concentration of 12 at% showed a leakage current reduced by one order of magnitude compared to un-doped BTO (i.e., ∼10 −7 to ∼10 −6 A/cm 2 at +1.6 V) without a significant drop of the dielectric constant (43,un-doped to 40, Al-doped).

Specimen preparation remains a practical challenge in transmission electron microscopy and frequently limits the quality of structural and chemical characterization data obtained. Prevailing methods for thinning of specimens to electron transparency are serial in nature, time consuming, and prone to producing artifacts and specimen failure. This work presents an alternative method for the preparation of plan-view specimens using isotropic vapor-phase etching with integrated etch stops. An ultrathin amorphous etch-stop layer simultaneously serves as an electron transparent support membrane whose thickness is defined by a controlled growth process such as atomic layer deposition with sub-nanometer precision. This approach eliminates the need for mechanical polishing or ion milling to achieve electron transparency, and reduces the occurrence of preparation induced artifacts. Furthermore, multiple specimens from a plurality of samples can be thinned in parallel due to high selectivity of the vapor-phase etching process. These features enable dramatic reductions in preparation time and cost without sacrificing specimen quality and provide advantages over wet etching techniques. Finally, we demonstrate a platform for high-throughput transmission electron microscopy of plan-view specimens by combining the parallel preparation capabilities of vapor-phase etching with wafer-scale micro- and nanofabrication.

We demonstrate stable, atomically smooth monolayer oxidation of Si(111) using a remote plasma. Scanning tunneling microscopy (STM) confirms the atomically flat nature of the oxidized surface, while cross-sectional transmission electron microscopy (TEM) proves the monolayer to bilayer oxide thickness. Fourier transform infrared spectroscopy (FTIR) and atomic layer deposition (ALD) indicate oxygen is incorporated onto the silicon surface in the form of Si–O–Si and Si–OH bonds. The incorporation of Si–OH bonds is inferred by using TiCl4, a highly specific ALD precursor, for TiO2 ALD. This plasma technique provides precise control of the surface chemistry and yields abrupt yet stable SiO/Si interfaces. It enables production of atomically flat, ALD-active silicon surfaces that could serve as a well-defined platform for investigation of various surface chemistries via STM. Using this substrate, we present the first ever STM observations of ALD TiO2 on silicon oxide.

This paper presents new results from the first thermal accelerometer fabricated using Plasma Enhanced Atomic Layer Deposition. PEALD allows for ultrathin high-density platinum films that deliver excellent stability and accuracy [1]. We offer a 100x cross-section reduction relative to previous thermal accelerometers, thereby increasing the heating efficiency and decreasing thermal time constants [2,3,4,5]. The resistance thermometers and heaters capitalize on the properties provided by PEALD and Pt: extreme stability, high resistivity, and linear temperature coefficient of resistance (TcR) [6]. For a heater temperature rise of 150°C, this device has a raw sensitivity of 54 moC/g, excellent cross-axis isolation, and remarkably low drift.

Plasma-enhanced atomic layer deposition (PEALD) provides multiple benefits compared to thermal ALD including lower possible process temperature and a wider palette of possible materials. However, coverage of high aspect ratio (AR) structures is limited due to the recombination rates of the radical plasma species. We study the limits of conformality in 1:30 AR structures for TiO2 based on tetrakis(dimethylamido)titanium (TDMA-Ti) and O2 plasma through variation in plasma exposure and substrate temperature. Extending plasma exposure duration and decreasing substrate temperature within the ALD window both serve to improve the conformality of the deposited film, with coverage >95% achievable. Additionally, the changes in morphology of the TiO2 were examined with crystallites of anatase and brookite found.

Aluminum doped HfO2 (HfAlO) prepared by atomic layer deposition is investigated as gate dielectric for low-voltage organic thin-film transistors (OTFTs). The HfAlO film exhibits a low leakage current density of \(4.92 \times 10^{-8}\) A/cm \(^{2}\) at −3 MV/cm, which is \(\sim 70\) % smaller than its HfO2 counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility \(\mu ~(2.58\pm 0.32\times 10^{-3}\) cm \(^{2}\) /Vs) increased by 58%, sub-threshold slope SS (0.9 ± 0.11 V/decade) decreased by 11%, and ON/OFF ratio \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}\) (3.1 ± 1.3 \(\times \) \( 10^{3}\) ) increased by 86% as compared with those with HfO2 as gate dielectric ( \(\mu =1.63\pm 0.27\times 10^{-3}\) cm \(^{2}\) /Vs; \({\rm SS}=1.01\) ±0.1 V/decade; \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}=1.7\pm 0.77\times 10^{3}\) ). All these could be ascribed to the inclusion of Al in the HfO2 film, which increases the conduction band offset and the bandgap and improves the dielectric and interface quality. The temperature effect on the performance of OTFTs is also investigated.

The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposited (ALD) of hydrofluoric acid (HF) etch resistant and electrically insulating films for sidewall spacer processing. Silicon nitride (SiN) has been the prototypical material for this need and extensive work has been conducted into realizing sufficiently lower wet etch rates (WERs) as well as leakage currents to meet industry needs. In this work, we report on the development of plasma-enhanced atomic layer deposition (PEALD) composites of SiN and AlN to minimize WER and leakage current density. In particular, the role of aluminum and the optimum amount of Al contained in the composite structures have been explored. Films with near zero WER in dilute HF and leakage currents density similar to pure PEALD SiN films could be simultaneously realized through composites which incorporate ≥13 at. % Al, with a maximum thermal budget of 350 °C.

Tetrakisdimethylamido (TDMA) based precursors are commonly used to deposit metal oxides such as TiO2, ZrO2, and HfO2 by means of chemical vapor deposition and atomic layer deposition (ALD). Both thermal and plasma enhanced ALD (PEALD) have been demonstrated with TDMA-metal precursors. While the reactions of TDMA-type precursors with water and oxygen plasma have been studied in the past, their reactivity with pure O2 has been overlooked. This paper reports on experimental evaluation of the reaction of molecular oxygen (O2) and several metal organic precursors based on TDMA ligands. The effect of O2 exposure duration and substrate temperature on deposition and film morphology is evaluated and compared to thermal reactions with H2O and PEALD with O2 plasma. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in (Journal of Vacuum Science and Technology A) and may be found at (http://avs.scitation.org/doi/10.1116/1.4937991). Licensed under a Creative Commons Attribution 3.0 Unported License. (CC BY 3.0 NO)

We report on the demonstration of a microfabrication process which allows the release of suspended films or structures of varying sizes in which the release volume is predefined by i) lithographic patterning, ii) etch-stop deposition by atomic layer deposition (ALD), iii) refilling sacrificial layer into the empty volume, and iv) subsequent chemical mechanical planarization (CMP). We refer to this as an “etch sandbox,” which allows the user to process devices on a planarized substrate after completion of the sandbox. We demonstrate micrometer scale Al2O3 suspended membranes utilizing Al 2 O 3 as the etch-stop and polysilicon as the refill/sacrificial etch material. Within a single substrate and single release, defined etch volumes up to differing by up to a factor of 104 can be realized. Considering the flexibility of this process, suspended membranes with more complicated structure and composition could be developed in the future.

NbTiN has a variety of superconducting applications, ranging from RF cavities to single-photon detectors. Here, we systematically investigated the plasma-enhanced atomic layer deposition (PEALD) of Nb x Ti with the organometallic precursors (t-butylimido) tris(diethyamido) niobium(V) and tetrakis (dimethylamido) titanium in conjunction with a remote H2/N2 plasma. Deposited film properties have been studied as a function of the ratio of Nb to Ti precursor pulses within each ALD supercycle. PEALD NbTiN films were characterized with spectroscopic ellipsometry (thickness, optical properties), four point probe (resistivity), x-ray photoelectron spectroscopy (composition), x-ray reflectivity (density and thickness), x-ray diffraction (crystallinity), and superconductivity measurements. The PEALD process has shown distinct advantages over deposition of superconducting films via thermal ALD or sputtering, for example a lower processing temperature and more efficient control of film composition. This control of film composition enabled the tuning of electrical and superconducting properties, such as varying the superconducting critical temperature T C between 6.9 and 13.2 K.

The accurate measurement of mechanical properties of thin films is required for the design of reliable nano/micro-electromechanical devices but is increasingly challenging for thicknesses approaching a few nanometers. We apply a combination of resonant and static mechanical test structures to measure elastic constants and residual stresses of 8–27 nm thick Al2O3 and Pt layers which have been fabricated through atomic layer deposition. Young's modulus of poly-crystalline Pt films was found to be reduced by less than 15% compared to the bulk value, whereas for amorphous Al2O3 it was reduced to about half of its bulk value. We observed no discernible dependence of the elastic constant on thickness or deposition method for Pt, but the use of plasma-enhanced atomic layer deposition was found to increase Young's modulus of Al2O3 by 10% compared to a thermal atomic layer deposition. As deposited, the Al2O3 layers had an average tensile residual stress of 131 MPa. The stress was found to be higher for thinner layers and layers deposited without the help of a remote plasma. No residual stress values could be extracted for Pt due to insufficient adhesion of the film without an underlying layer to promote nucleation.

Thin films of niobium nitride are useful for their physical, chemical, and electrical properties. NbN superconducting properties have been utilized in a wide range of applications. Plasma-enhanced atomic layer deposition (PEALD) of NbN with (t-butylimido) tris(diethylamido) niobium(V) and remote H2/N2 plasmas has been investigated. Deposited film properties have been studied as a function of substrate temperature (100–300 °C), plasma power (150–300 W), and H2 flow rate (10–80 sccm). PEALD NbN films were characterized with spectroscopic ellipsometry (thickness, optical properties), four point probe (resistivity), x-ray photoelectron spectroscopy (composition), x-ray reflectivity (density and thickness), x-ray diffraction (crystallinity), and superconductivity measurements. Film composition varied with deposition conditions, but larger cubic NbN crystallites and increased film density at higher substrate temperatures and H2 flow rates lead to room temperature resistivity values as low as 173 μΩ cm and super...

We evaluated the chemical and electrochemical corrosion resistance of ultra-thin films deposited via atomic layer deposition (ALD) for potential wafer-scale passivation of biomedical microdevices. A variety of ALD coatings can be deposited conformally on metal or silicon surfaces at low temperature. We were able to protect aluminum electrodes against corrosion in ionic media with a voltage stress of 1V for 200 hours using a double ALD film stack of 5nm Al2O3 and 5nm HfO2.

Laterally actuated nanoelectromechanical relays with compliant source-drain contacts are presented. The relay sidewalls are coated with a 30 nm-thick conductive layer of titanium nitride (TiN) deposited using atomic layer deposition (ALD). By hollowing the tip of the relay, a flexible sidewall is formed from the thin TiN that results in a larger contact area and therefore improves the contact properties of the relay. This modification improves the on-state resistance (RON) and also provides better stability over a larger number of switching cycles compared to a rigid contact. The results of life-time tests show that the contact resistance increases with the number of switching cycles possibly due to degradation of the contact material. However, flexible contacts show improved contact resistance stability under cyclic contact.

We report the realization of coalescent free-standing ultra-thin (as thin as 5.5 nm) platinum layers deposited via plasma-enhanced atomic layer deposition and their characterization as an uncooled infrared detector. Such thin platinum thermistors enable a responsivity as high as 2 · 107 V/WA, an estimated noise equivalent temperature difference of 163 mK and thermal time constants on the order of 1 ms.

CuPc-based organic thin-film transistor (OTFT) with high-k dielectric HfAlO as gate dielectric prepared by atomic layer deposition has been fabricated. Experimental results show that the HfAlO-OTFT has higher mobility, smaller sub-threshold slope and larger on/off ratio than the HfO 2 sample. All these should be attributed to the addition of Al into the HfO 2 film confirmed by X-ray photoelectron spectroscopy, resulting in improved dielectric and interfacial properties. Moreover, the reliablity of the device upon exposure to air is investigated.

Tungsten nitride (WN) has potential as an interconnect barrier film. Deposition of WN films with bis(tert-butylimido)bis(dimethylamido)tungsten utilizing plasma-enhanced atomic layer deposition has been investigated over a temperature range of 100–400 °C employing N2, H2/N2, and NH3 remote plasmas. Spectroscopic ellipsometry has been used to determine film thickness and optical properties. Film growth rate varied from 0.44 to 0.65 A/cycle. Chemical composition was investigated with x-ray photoelectron spectroscopy. W:N ratios varied from 0.95:1 to 3.76:1 and carbon levels were sub-2% for atomic layer deposition conditions. Resistivity measurements, derived from four-point probe measurements, indicate higher deposition temperature and gas flow rates produce the lowest resistivity films. The lowest resistivity film of the study, which measured 405 μΩ cm, was deposited with a hydrogen-rich H2/N2 plasma at 400 °C.

The continued scaling in transistors and memory elements has necessitated the development of atomic layer deposition (ALD) of silicon nitride (SiNx), particularly for use a low k dielectric spacer. One of the key material properties needed for SiNx films is a low wet etch rate (WER) in hydrofluoric (HF) acid. In this work, we report on the evaluation of multiple precursors for plasma enhanced atomic layer deposition (PEALD) of SiNx and evaluate the film’s WER in 100:1 dilutions of HF in H2O. The remote plasma capability available in PEALD, enabled controlling the density of the SiNx film. Namely, prolonged plasma exposure made films denser which corresponded to lower WER in a systematic fashion. We determined that there is a strong correlation between WER and the density of the film that extends across multiple precursors, PEALD reactors, and a variety of process conditions. Limiting all steps in the deposition to a maximum temperature of 350 °C, it was shown to be possible to achieve a WER in PEALD SiNx of 6.1 Å/min, which is similar to WER of SiNx from LPCVD reactions at 850 °C.

While the literature is rich with data for the electrical behavior of nanotransistors based on semiconductor nanowires and carbon nanotubes, few data are available for ultrascaled metal interconnects that will be demanded by these devices. Atomic layer deposition (ALD), which uses a sequence of self-limiting surface reactions to achieve high-quality nanolayers, provides an unique opportunity to study the limits of electrical and thermal conduction in metal interconnects. This work measures and interprets the electrical and thermal conductivities of free-standing platinum films of thickness 7.3, 9.8, and 12.1 nm in the temperature range from 50 to 320 K. Conductivity data for the 7.3 nm bridge are reduced by 77.8% (electrical) and 66.3% (thermal) compared to bulk values due to electron scattering at material and grain boundaries. The measurement results indicate that the contribution of phonon conduction is significant in the total thermal conductivity of the ALD films.

Laterally actuated nanoelectromechanical (NEM) relays are implemented using a polysilicon structural layer with hafnium oxide (HfO 2 ) and platinum dual sidewall layers. Atomic layer deposition (ALD) HfO 2 provides electrical isolation between the polysilicon beam structure and the sputtered platinum conductive channel. Dual sidewall devices are demonstrated using a Y-shaped device with two contacts that connect source and drain upon actuation. Fabricated devices show up to 1µA current passing between source and drain without beam current flow, confirming successful isolation.

HfO x /AlO x bi-layer RRAM devices were fabricated with the atomic layer deposition (ALD) method. Compared with the single-layer HfO x devices, the bi-layer devices showed less variation of the switching voltages and resistances. Inspired by the fact that varying reset stop voltage in a DC sweep can achieve multilevel high resistance state, two equivalent pulse programming schemes were proposed: one linearly increases the reset pulse amplitudes; the other exponentially increases the reset pulse width. The transient current response waveform measurement suggests the former scheme is a more energy efficient programming method.

This paper presents an uncooled infrared bolometer using a metal thin film that is formed by atomic layer deposition (ALD). Nanometer-thick freestanding layers enabled by ALD have the potential to improve the performance of bolometers with achieving low thermal conductance and near optimal optical properties. The fabrication and characterization of the first implementation are described as well as the electrical properties of ALD platinum films.