Tungsten (W) films have many applications in the semiconducting industry for sensor technology. Deposition conditions can significantly impact the resulting W films in terms of the phases present (α-BCC or β-A12), microstructural grain orientation (texture), and residual strain. Tilt-A-Whirl methodology has been employed for the evaluation of a W film showing both texture and residual strain. Sin2(ψ) analysis of the film was performed to quantify the strongly tensile in-plane strain (+0.476%) with an estimated in-plane tensile stress of ~1.9 GPa. The 3D dataset was also evaluated qualitatively via 3D visualization. Visualization of 3D texture/strain data poses challenges due to peak broadening resulting from defocusing of the beam at high ψ tilt angles. To address this issue, principal component analysis (PCA) was employed to diagnose, model, and remove the broadening component from the diffraction data. Evaluation of the raw data and subsequent corrected data (after removal of defocusing effects) has been performed through projection of the data into a virtual 3D environment (via CAD2VR software) to qualitatively detect the impact of residual strain on the observed pole figure.
This work demonstrated both NbN and Nb make good electrodes for stabilizing orthorhombic phase of Hf0.6Zr0.4O2 ferroelectric films. Wake up are < 100 cycles. Pr can be as high as 30 µC/cm2 - respectively 14 and 18 µC/cm2 here. Further, capacitance suggests an orthorhombic phase can be stabilized. Addition of a linear dielectric under modest thickness can tune the Pr and reduce leakage.
Ferroelectric phase stability in hafnium oxide is reported to be influenced by factors that include composition, biaxial stress, crystallite size, and oxygen vacancies. In the present work, the ferroelectric performance of atomic layer deposited Hf0.5Zr0.5O2 (HZO) prepared between TaN electrodes that are processed under conditions to induce variable biaxial stresses is evaluated. The post-processing stress states of the HZO films reveal no dependence on the as-deposited stress of the adjacent TaN electrodes. All HZO films maintain tensile biaxial stress following processing, the magnitude of which is not observed to strongly influence the polarization response. Subsequent composition measurements of stress-varied TaN electrodes reveal changes in stoichiometry related to the different preparation conditions. HZO films in contact with Ta-rich TaN electrodes exhibit higher remanent polarizations and increased ferroelectric phase fractions compared to those in contact with N-rich TaN electrodes. HZO films in contact with Ta-rich TaN electrodes also have higher oxygen vacancy concentrations, indicating that a chemical interaction between the TaN and HZO layers ultimately impacts the ferroelectric orthorhombic phase stability and polarization performance. The results of this work demonstrate a necessity to carefully consider the role of electrode processing and chemistry on performance of ferroelectric hafnia films.
We report experimental and numerical developments extending the operating range of vanadium dioxide based optical limiters into the short-wavelength infrared. Pixelated sensor elements have been fabricated which show optically-triggered limiting of a 2.7 µm probe.
We report on the fabrication and characterization of Nb/Ta-N/Nb Josephson junctions grown by room temperature magnetron sputtering on 150-mm diameter Si wafers. Junction characteristics depend upon the Ta-N barrier composition, which was varied by adjusting the N2 flow during film deposition. Higher N2 flow rates raise the barrier resistance and increase the junction critical current. This work demonstrates the viability of Ta-N as an alternative barrier to aluminum oxide, with the potential for large scale integration.
Maximum power handling, spike leakage, and failure mechanisms have been characterized for limiters based on the thermally triggered metal-insulator transition of vanadium dioxide. These attributes are determined by properties of the metal-insulator material such as on/off resistance ratio, geometric properties that determine the film resistance and the currentcarrying capability of the device, and thermal properties such as heatsinking and thermal coupling. A limiter with greater than 10 GHz of bandwidth demonstrated 0.5 dB loss, 27 dBm threshold power, 8 Watts blocking power, and 0.4 mJ spike leakage at frequencies near 2 GHz. A separate limiter optimized for high power blocked over 60 Watts of incident power with leakage less than 25 dBm after triggering. The power handling demonstrates promise for these limiter devices, and device optimization presents opportunities for additional improvement in spike leakage, response speed, and reliability.
We have developed an ambient temperature, SiO2/Si wafer - scale process for Josephson junctions based on Nb electrodes and Ta x N barriers with tunable electronic properties. The films are fabricated by magnetron sputtering. The electronic properties of the TaxN barriers are controlled by adjusting the nitrogen flow during sputtering. This technology offers a scalable alternative to the more traditional junctions based on AlOx barriers for low - power, high - performance computing.
Properties of NbN and TaxN thin films grown at ambient temperatures on SiO2/Si substrates by reactive-pulsed laser deposition and reactive magnetron sputtering (MS) as a function of N2 gas flow were investigated. Both techniques produced films with smooth surfaces, where the surface roughness did not depend on the N2 gas flow during growth. High crystalline quality, (111) oriented NbN films with Tc up to 11 K were produced by both techniques for N contents near 50%. The low temperature transport properties of the TaxN films depended upon both the N2 partial pressure used during growth and the film thickness. The root mean square surface roughness of TaxN films grown by MS increased as the film thickness decreased down to 10 nm.
Niobium and niobium nitride thin films are transitioning from fundamental research toward wafer scale manufacturing with technology drivers that include superconducting circuits and electronics, optical single photon detectors, logic, and memory. Successful microfabrication requires precise control over the properties of sputtered superconducting films, including oxidation. Previous work has demonstrated the mechanism in oxidation of Nb and how film structure could have deleterious effects upon the superconducting properties. This study provides an examination of atmospheric oxidation of NbN films. By examination of the room temperature sheet resistance of NbN bulk oxidation was identified and confirmed by secondary ion mass spectrometry. As a result, Meissner magnetic measurements confirmed the bulk oxidation not observed with simple cryogenic resistivity measurements.
The locations of conductive regions in TaOx memristors are spatially mapped using a microbeam and Nanoimplanter by rastering an ion beam across each device while monitoring its resistance. Microbeam irradiation with 800 keV Si ions revealed multiple sensitive regions along the edges of the bottom electrode. The rest of the active device area was found to be insensitive to the ion beam. Nanoimplanter irradiation with 200 keV Si ions demonstrated the ability to more accurately map the size of a sensitive area with a beam spot size of 40 nm by 40 nm. Isolated single spot sensitive regions and a larger sensitive region that extends approximately 300 nm were observed.
The human brain (volume=1200cm3) consumes 20W and is capable of performing > 10^16 operations/s. Current supercomputer technology has reached 1015 operations/s, yet it requires 1500m^3 and 3MW, giving the brain a 10^12 advantage in operations/s/W/cm^3. Thus, to reach exascale computation, two achievements are required: 1) improved understanding of computation in biological tissue, and 2) a paradigm shift towards neuromorphic computing where hardware circuits mimic properties of neural tissue. To address 1), we will interrogate corticostriatal networks in mouse brain tissue slices, specifically with regard to their frequency filtering capabilities as a function of input stimulus. To address 2), we will instantiate biological computing characteristics such as multi-bit storage into hardware devices with future computational and memory applications. Resistive memory devices will be modeled, designed, and fabricated in the MESA facility in consultation with our internal and external collaborators.
This paper describes the development and implementation of an integrated resistor process based on reactively sputtered tantalum nitride. Image reversal lithography was shown to be a superior method for liftoff patterning of these films. The results of a response surface DOE for the sputter deposition of the films are discussed. Several approaches to stabilization baking were examined and the advantages of the hot plate method are shown. In support of a new capability to produce special-purpose HBT-based Small-Scale Integrated Circuits (SSICs), we developed our existing TaN resistor process, designed for research prototyping, into one with greater maturity and robustness. Included in this work was the migration of our TaN deposition process from a research-oriented tool to a tool more suitable for production. Also included was implementation and optimization of a liftoff process for the sputtered TaN to avoid the complicating effects of subtractive etching over potentially sensitive surfaces. Finally, the method and conditions for stabilization baking of the resistors was experimentally determined to complete the full implementation of the resistor module. Much of the work to be described involves the migration between sputter deposition tools - from a Kurt J. Lesker CMS-18 to a Denton Discovery 550. Though they use nominally the same deposition technique (reactive sputtering of Ta with N{sup +} in a RF-excited Ar plasma), they differ substantially in their design and produce clearly different results in terms of resistivity, conformity of the film and the difference between as-deposited and stabilized films. We will describe the design of and results from the design of experiments (DOE)-based method of process optimization on the new tool and compare this to what had been used on the old tool.
We designed, fabricated and measured the performance of nanoelectromechanical (NEMS) switches. Initial data are reported with one of the switch designs having a measured switching time of 400 ns and an operating voltage of 5 V. The switches operated laterally with unmeasurable leakage current in the 'off' state. Surface micromachining techniques were used to fabricate the switches. All processing was CMOS compatible. A single metal layer, defined by a single mask step, was used as the mechanical switch layer. The details of the modeling, fabrication and testing of the NEMS switches are reported.