K. B. Jinesh

Ultrahigh Capacitance Density for Multiple ALD-Grown MIM Capacitor Stacks in 3-D Silicon

ldquoTrenchrdquo capacitors containing multiple metal-insulator-metal (MIM) layer stacks are realized by atomic-layer deposition (ALD), yielding an ultrahigh capacitance density of 440 at a breakdown voltage VDB > 6 V. This capacitance density on silicon is at least 10times higher than the values reported by other research groups. On a silicon substrate containing high-aspect-ratio macropore arrays, alternating MIM layer stacks comprising high-k Al2O3dielectrics and TiN electrodes are deposited using optimized ALD processing such that the conductivity of the TiN layers is not attacked. Ozone annealing subsequent to each Al2O3 deposition step yields significant improvement of the dielectric isolation and breakdown properties.

Plasma-assisted atomic layer deposition of TiN/Al2O3 stacks for metal-oxide-semiconductor capacitor applications

By employing plasma-assisted atomic layer deposition, thin films of Al2O3 and TiN are subsequently deposited in a single reactor at a single substrate temperature with the objective of fabricating high-quality TiN/Al2O3/p-Si metal-oxide-semiconductor capacitors. Transmission electron microscopy and Rutherford backscattering spectroscopy analyses show well-defined interfaces and good Al2O3 stoichiometry, respectively. Electrical investigation of as-deposited test structures demonstrates leakage current densities as low as ∼1 nA/cm2. Current-voltage (I-V) measurements demonstrate clear Fowler–Nordheim tunneling with an average TiN/Al2O3 barrier height of 3.3 eV. Steep Weibull distributions of the breakdown electric field around 7.5 MV/cm indicate good reliability of these devices. Time-dependent dielectric breakdown measurements demonstrate that the devices can sustain high operating electric fields of 3–4 MV/cm for the 10 year lifetime criterion. From capacitance-voltage (C-V) measurements, a dielectric co...

RF Characterization and Analytical Modelling of Through Silicon Vias and Coplanar Waveguides for 3D Integration

High-aspect ratio (12.5) through silicon vias (TSV) made in a silicon interposer have been electrically characterized in the direct current (dc) and microwave regimes for 3D interconnect applications. The vias were micro-machined in silicon, insulated, and filled with copper employing a bottom-up copper electroplating technique in a “via-first” approach. DC via resistance measurements show good agreement with the theoretical expected value (~ 16 mΩ) . Radio-frequency (RF) measurements up to 50 GHz have been performed on coplanar waveguides located on the back-side of the wafers and connected to the front-side with TSVs. The S-parameters indicate clearly the beneficial impact of double sided ground planes of the RF signals. The via resistance extracted from impedance measurements is in good agreement with dc values, while the inductance (53 pH) and capacitance (2.4 pF) of the TSV are much lower than conventional wire bonding, which makes the use of TSV very promising for 3D integration. An advanced analytical model is proposed for the interconnect system with vias and lines and shows very good agreement with the experimental data with a limited number of fitting parameters. This work gives a proof of concept for high aspect ratio TSV manufacturing and new insights to improve 3D interconnect modeling for systems-in-package applications in the microwave regime.

Low temperature synthesis of wurtzite zinc sulfide (ZnS) thin films by chemical spray pyrolysis

Zinc sulfide (ZnS) thin films have been synthesized by spray pyrolysis at 310 °C using an aqueous solution of zinc chloride (ZnCl2) and thioacetamide (TAA). Highly crystalline films were obtained by applying TAA instead of thiourea (TU) as the sulfur source. X-ray diffraction (XRD) analyses show that the films prepared by TAA contained a wurtzite structure, which is usually a high temperature phase of ZnS. The crystallinity and morphology of the ZnS films appeared to have a strong dependence on the spray rate as well. The asymmetric polar structure of the TAA molecule is proposed to be the intrinsic reason of the formation of highly crystalline ZnS at comparatively low temperatures. The violet and green emissions from photoluminescence (PL) spectroscopy reflected the sulfur and zinc vacancies in the film. Accordingly, the photodetectors fabricated using these films exhibit excellent response to green and red photons of 525 nm and 650 nm respectively, though the band gaps of the materials, estimated from optical absorption spectroscopy, are in the range of 3.5-3.6 eV.

Electrical and photoresponse properties of Co3O4 nanowires

Electrical and photocurrent characteristics of single Co3O4 nanowire devices were studied systematically. Current-voltage characteristics’ measurements and impedance spectroscopy of single Co3O4 nanowire devices were performed and analysed using possible mechanism. Photoresponses of individual nanowires were obtained by global irradiation of laser beams with photon energies above band gap and at sub-band gap of the nanowires. The magnitude of photocurrent and its response time revealed that defect level excitations significantly contribute to the photoresponse of Co3O4 nanowires. In addition, the electrically Ohmic nature of the nanowire/Pt contact and p-type conductivity of Co3O4 nanowire is extracted from the current-voltage characteristics and spatially resolved photocurrent measurements.

Dielectric Properties of Thermal and Plasma-Assisted Atomic Layer Deposited Al2O3 Thin Films

A comparative electrical characterization study of aluminum oxide (Al2O3) deposited by thermal and plasma-assisted atomic layer depositions (ALDs) in a single reactor is presented. Capacitance and leakage current measurements show that the Al2O3 deposited by the plasma-assisted ALD shows excellent dielectric properties, such as better interfaces with silicon, lower oxide trap charges, higher tunnel barrier with aluminum electrode, and better dielectric permittivity (k = 8.8), than the thermal ALD Al2O3. Remarkably, the plasma-assisted ALD Al2O3 films exhibit more negative fixed oxide charge density than the thermal ALD Al2O3 layers. In addition, it is shown that plasma-assisted ALD Al2O3 exhibits negligible trap-assisted (Poole-Frenkel) conduction unlike the thermal ALD Al2O3 films, resulting in higher breakdown electric fields than the thermal ALD prepared films

Charge conduction mechanisms of atomic-layer-deposited Er2O3 thin films

The charge transport mechanism through atomic-layer-deposited erbium oxide thin films has been analyzed with current-voltage (I-V) measurements. At low electric field, i.e., below 3 MV/cm, the charge conduction through 10 nm thick Er2O3 films is dominated by Poole–Frenkel electron injection. However, Fowler–Nordheim tunneling of holes also occurs at higher electric fields through the oxide. Various electronic and material parameters such as the trap density, activation energy of the traps, and interface defect density are extracted from the I-V and parallel conductance (GP) measurements as a function of frequency.

Maxwell–Wagner instability in bilayer dielectric stacks

The Maxwell–Wagner effect, the enhanced charge migration to the interface of a stack of two dielectrics with different conductances, is shown to cause asymmetric leakage current and electrical breakdown behavior for different electrode polarities. For this purpose, metal-insulator-silicon capacitors were fabricated consisting of bilayered silicon dioxide–lanthanum zirconate dielectric stacks. Maxwell–Wagner instability and Debye polarization can be distinguished upon comparing electron injection from both sides of the stack. The Maxwell–Wagner charges have relaxation times that are nearly five orders of magnitude larger than the Debye polarization, suggesting the long-lasting influence of these trapped charges in nanolaminated dielectric systems.The Maxwell–Wagner effect, the enhanced charge migration to the interface of a stack of two dielectrics with different conductances, is shown to cause asymmetric leakage current and electrical breakdown behavior for different electrode polarities. For this purpose, metal-insulator-silicon capacitors were fabricated consisting of bilayered silicon dioxide–lanthanum zirconate dielectric stacks. Maxwell–Wagner instability and Debye polarization can be distinguished upon comparing electron injection from both sides of the stack. The Maxwell–Wagner charges have relaxation times that are nearly five orders of magnitude larger than the Debye polarization, suggesting the long-lasting influence of these trapped charges in nanolaminated dielectric systems.

Characterization and Modeling of Atomic Layer Deposited High-Density Trench Capacitors in Silicon

A detailed electrical analysis of multiple layer trench capacitors fabricated in silicon with atomic-layer-deposited <i>Al</i>₂<i>O</i>₃ and <i>TiN</i> is presented. It is shown that in situ ozone annealing of the <i>Al</i>₂<i>O</i>₃ layers prior to the <i>TiN</i> electrode deposition significantly improves the electric properties of the devices such as the dielectric constant, leakage current, and the breakdown voltage of the devices. The self-inductance and self-resistance of the capacitors as derived from <i>S</i>-parameter measurements up to 10 GHz are very small, as low as 4 pH and 6 mΩ for 19.1 mm² electrode surface. These data are shown to be consistent with a theoretical model.

How quantum confinement comes in chemically deposited CdS?—A detailed XPS investigation

Abstract Chemically deposited thin films of cadmium sulfide (CdS) nanoparticles are analyzed using different techniques to estimate the origin of quantum confinements of CdS clusters in the film. The increase of Cd(OH)2 in the sample with the increase of pH of the bath, observed in XPS depth profiles, depicts the possibility that the CdS clusters of finite size are embedded in Cd(OH)2 surroundings, which ultimately makes the clusters electrically isolated and hence providing carrier confinements. X-ray diffraction and optical absorption studies on these films indicated clear clustering and subsequent carrier confinement effects. An XPS of the same film, after 1 month, shows the conversion of surface layers of Cd(OH)2 into CdO, which is rather a conducting compound.