Markus D. Groner

Viscous flow reactor with quartz crystal microbalance for thin film growth by atomic layer deposition

A chemical reactor was constructed for growing thin films using atomic layer deposition (ALD) techniques. This reactor utilizes a viscous flow of inert carrier gas to transport the reactants to the sample substrates and to sweep the unused reactants and reaction products out of the reaction zone. A gas pulse switching method is employed for introducing the reactants. An in situ quartz crystal microbalance (QCM) in the reaction zone is used for monitoring the ALD film growth. By modifying a commercially available QCM housing and using polished QCM sensors, quantitative thickness measurements of the thin films grown by ALD are obtained in real time. The QCM is employed to characterize the performance of the viscous flow reactor during Al2O3 ALD.

Ca test of Al2O3 gas diffusion barriers grown by atomic layer deposition on polymers

Quantitative Ca tests were used to determine the water vapor transmission rate (WVTR) through 25nm thick Al2O3 gas diffusion barriers grown on plastic by atomic layer deposition (ALD). The measured WVTRs were 1.7×10−5g∕m2day at 38°C and 6.5×10−5g∕m2day at 60°C. Based on the apparent activation energy, the WVTR at 23°C is estimated to be only 6×10−6g∕m2day. The WVTR values for the Al2O3 ALD film are very similar to the WVTR value for the glass control. These Ca tests indicate that Al2O3 ALD gas diffusion barriers should enable display and lighting applications of highly moisture sensitive organic light-emitting diodes on plastic.

Ultrathin Direct Atomic Layer Deposition on Composite Electrodes for Highly Durable and Safe Li‐Ion Batteries

Abstract : In order to employ Li-ion batteries (LIBs) in next-generation hybrid electric and/or plug-in hybrid electric vehicles (HEVs and PHEVs), LIBs must satisfy many requirements: electrodes with long lifetimes (fabricated from inexpensive environmentally benign materials), stability over a wide temperature range, high energy density, and high rate capability. Establishing long-term durability while operating at realistic temperatures (5000 charge-depleting cycles, 15 year calendar life, and a range from -46 deg C to +66 deg C) for a battery that does not fail catastrophically remains a significant challenge. Recently, surface modifications of electrode materials have been explored as viable paths to improve the performance of LIBs for vehicular applications. Here we clearly demonstrate that conformal ultrathin protective coating by inactive metal oxide without disrupting inter-particle electronic pathway can be realized by atomic layer deposition (ALD) directly performed on a composite electrode, which leads to significant improvement of both long-term durability and safety of NG anode. Also ALD coatings are significantly more promising than efforts that have been previously reported.

Gas diffusion barriers on polymers using Al2O3 atomic layer deposition

Thin films of Al2O3 grown by atomic layer deposition (ALD) were investigated as gas diffusion barriers on flexible polyethylene naphthalate and Kapton® polyimide substrates. Al2O3 ALD films with thicknesses of 1–26nm were grown at 100–175°C. For Al2O3 ALD films with thicknesses ⩾5nm, oxygen transmission rates were below the MOCON instrument test limit of ∼5×10−3cc∕m2∕day. Applying a more sensitive radioactive tracer method, H2O-vapor transmission rates of ∼1×10−3g∕m2∕day were measured for single-sided Al2O3 ALD films with thicknesses of 26nm on the polymers. Ultrathin gas diffusion barriers grown by Al2O3 ALD may enable organic displays and electronics on permeable, flexible polymer substrates.

Enhanced Stability of LiCoO2 Cathodes in Lithium-Ion Batteries Using Surface Modification by Atomic Layer Deposition

Ultrathin atomic layer deposition (ALD) coatings enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO 2 cathode powders coated with metal oxides with thicknesses of ∼100 to 1000 A grown using wet chemical techniques improved LIB performance. In this study, LiCoO 2 powders were coated with conformal Al 2 O 3 ALD films with thicknesses of only ∼ 3 to 4 A established using two ALD cycles. The coated LiCoO 2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V (vs Li/Li + ) range. In contrast, the bare LiCoO 2 powders displayed only a 45% capacity retention. Al 2 O 3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al 2 O 3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance.

Gas diffusion ultrabarriers on polymer substrates using Al2O3 atomic layer deposition and SiN plasma-enhanced chemical vapor deposition

Thin films grown by Al2O3 atomic layer deposition (ALD) and SiN plasma-enhanced chemical vapor deposition (PECVD) have been tested as gas diffusion barriers either individually or as bilayers on polymer substrates. Single films of Al2O3 ALD with thicknesses of ≥10 nm had a water vapor transmission rate (WVTR) of ≤5×10−5 g/m2 day at 38 °C/85% relative humidity (RH), as measured by the Ca test. This WVTR value was limited by H2O permeability through the epoxy seal, as determined by the Ca test for the glass lid control. In comparison, SiN PECVD films with a thickness of 100 nm had a WVTR of ∼7×10−3 g/m2 day at 38 °C/85% RH. Significant improvements resulted when the SiN PECVD film was coated with an Al2O3 ALD film. An Al2O3 ALD film with a thickness of only 5 nm on a SiN PECVD film with a thickness of 100 nm reduced the WVTR from ∼7×10−3 to ≤5×10−5 g/m2 day at 38 °C/85% RH. The reduction in the permeability for Al2O3 ALD on the SiN PECVD films was attributed to either Al2O3 ALD sealing defects in the SiN PE...

Protecting Polymers in Space with Atomic Layer Deposition Coatings

Polymers in space may be subjected to a barrage of incident atoms, photons, and/or ions. Atomic layer deposition (ALD) techniques can produce films that mitigate many of the current challenges for space polymers. We have studied the efficacy of various ALD coatings to protect Kapton polyimide, FEP Teflon, and poly(methyl methacrylate) films from atomic-oxygen and vacuum ultraviolet (VUV) attack. Atomic-oxygen and VUV studies were conducted with the use of a laser-detonation source for hyperthermal O atoms and a D2 lamp as a source of VUV light. These studies used a quartz crystal microbalance (QCM) to monitor mass loss in situ, as well as surface profilometry and scanning electron microscopy to study the surface recession and morphology changes ex situ. Al2O3 ALD coatings protected the underlying substrates from atomic-oxygen attack, and the addition of TiO2 coatings protected the substrates from VUV-induced damage. The results indicate that ALD coatings can simultaneously protect polymers from oxygen-atom erosion and VUV radiation damage.

Enhanced Stability of LiCoO 2 Cathodes in Lithium-ion Batteries Using Surface Modification by Atomic Layer Deposition

Ultrathin atomic layer deposition (ALD) coatings were found to enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that LiCoO₂ cathode powders coated with metal oxides with thicknesses of ~100-1000 A grown using wet chemical techniques improved LIB performance. In this study, LiCoO₂ powders were coated with conformal Al₂O₃ ALD films with thicknesses of only ~3-4 A established using 2 ALD cycles. The coated LiCoO₂ powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3~4.5 V (vs. Li/Li?) range. In contrast, the bare LiCoO₂ powders displayed only a 45% capacity retention. This dramatic improvement may result from the ultrathin Al₂O₃ ALD film acting to minimize Co dissolution or to reduce surface electrolyte reactions.

Ultrafast metal-insulator varistors based on tunable Al2O3 tunnel junctions

Ultrafast metal-insulator varistors have been fabricated using atomic layer deposition. A high-density matrix of micron-sized spherical Ni particles conformally coated with ∼7.5–22nm Al2O3 films exhibited transient response times (∼0.3ns), capacitances (∼45pF), leakage currents (∼33pA), and nonlinearities (α∼380) which were all markedly improved over conventional metal oxide varistors. These characteristics result from the Fowler–Nordheim tunneling of electrons through uniform Al2O3 tunnel junctions separating adjacent particles within the matrix.

High- k dielectrics grown by atomic layer deposition: Capacitor and gate applications

Publisher Summary This chapter reviews the dramatic improvements in microelectronics performance over that past few decades that have been accompanied by a severe reduction in the size of memory and logic devices. This scaling required drastic decreases of the SiO2 dielectric film thickness to achieve ever-higher capacitance densities. Fundamental limits of SiO2 as a dielectric material, imposed by electron tunneling, reach SiO2 film thickness approaches ∼1 nm. High-κ interlayer dielectric material needs to replace SiO2 as a capacitor and gate dielectric material. Numerous alternate high-κ materials are being actively investigated, ranging from Al2O3 (k∼9) to perovskites (κ∼102–104), and achieves very high capacitance densities with relatively thick films. The thicker films preclude the excessive tunneling currents observed for very thin SiO2 films. Finding a high-κ material is a major challenge because the high-κ materials have a high resistivity, and act as a good barrier layer, which is thermally stable, and form an ideal interface with silicon. SiO2 films can be conveniently formed via oxidation of the silicon substrate. Alternate high-κ materials must be formed by deposition. Atomic layer deposition (ALD) is a promising technique for depositing alternate high-κ thin films for the microelectronics industry. ALD is also very well suited for depositing various types of composites that combine the desirable properties of different materials.Publisher Summary This chapter reviews the dramatic improvements in microelectronics performance over that past few decades that have been accompanied by a severe reduction in the size of memory and logic devices. This scaling required drastic decreases of the SiO2 dielectric film thickness to achieve ever-higher capacitance densities. Fundamental limits of SiO2 as a dielectric material, imposed by electron tunneling, reach SiO2 film thickness approaches ∼1 nm. High-κ interlayer dielectric material needs to replace SiO2 as a capacitor and gate dielectric material. Numerous alternate high-κ materials are being actively investigated, ranging from Al2O3 (k∼9) to perovskites (κ∼102–104), and achieves very high capacitance densities with relatively thick films. The thicker films preclude the excessive tunneling currents observed for very thin SiO2 films. Finding a high-κ material is a major challenge because the high-κ materials have a high resistivity, and act as a good barrier layer, which is thermally stable, and form an ideal interface with silicon. SiO2 films can be conveniently formed via oxidation of the silicon substrate. Alternate high-κ materials must be formed by deposition. Atomic layer deposition (ALD) is a promising technique for depositing alternate high-κ thin films for the microelectronics industry. ALD is also very well suited for depositing various types of composites that combine the desirable properties of different materials.