In this paper, we explore new metal electrodes for ferroelectric capacitors based on Al-doped HfO ₂ . We find that Ti/Pd, Ti/Au, and W top electrodes can induce much higher remanent polarization as compared to the traditional TiN top electrode. The endurance of the capacitors with Ti/Pd electrodes is also much better than that with TiN and W electrodes. These results indicate that Ti/Pd is a very promising candidate for ferroelectric Al-doped HfO ₂ . In addition, we find that the remanent polarization reaches maximum when the annealing temperature is around 900 °C–950 °C. At a given annealing temperature, the optimal Hf-to-Al cycle ratio corresponding to the highest remanent polarization is around 23:1. With optimized process conditions, we demonstrate high-performance Ti/Pd gated ferroelectric Al-doped HfO ₂ capacitors with remanent polarization up to $20~\mu \text{C}$ /cm ² , endurance higher than 10 ⁸ cycles, and retention over ten years at room temperature. Another interesting feature of the ferroelectric capacitors with Ti/Pd electrodes is high tunability of polarization by external pulses, which will be important for neurosynaptic computing applications.

Precision photoablation of bulk polymers or films with incoherent vacuum ultraviolet (VUV) radiation from flat, microplasma array-powered lamps has led to the realization of a photolithographic process in which an acrylic, polycarbonate, or other polymer serves as a dry photoresist. Patterning of the surface of commercial-grade, bulk polymers (or films spun onto Si substrates) such as poly-methyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) with 172 nm lamp intensities as low as ~10 mW/cm² and a fused silica contact mask yields trenches, as well as arbitrarily-complex 3D structures, with depths reproducible to ~10 nm. For 172 nm intensities of 10 mW/cm² at the substrate, linearized PMMA photoablation rates of ~4 nm/s are measured for exposure times t≤70 s but a gradual decline is observed thereafter. Beyond t~300 s, the polymer removal rate gradually saturates at ~0.2 nm/s. Intricate patterns are readily produced in bulk acrylics or 40-200 nm thick acrylic films on Si with two or more exposures and overall process times of typically 10-300 s. The photoablation process is sufficiently precise that the smallest lateral feature size fabricated reproducibly to date, ~350 nm, appears to be limited primarily by the photomask itself. Examples of the versatility and precision of this photolithographic process include the fabrication of arrays of aluminum nanomirrors, each atop a 350 nm or 1 μm-diameter Si post, as well as optical components such as transmission gratings or Fresnel lenses photoablated into PMMA.

A series of miniature, microcavity plasma lamps emitting predominantly at 194 nm has been successfully developed and tested as the optical pump for the microwave ¹⁹⁹ Hg-ion atomic clock (40.507 GHz), replacing low pressure, RF-powered Ar/Hg discharges. Intense fluorescence on the 6 p ² P _1/2 → 6 s ² S _1/2 transition of the singly-charged ²⁰² Hg ion at 194.23 nm has been generated in arrays of cylindrical microplasmas through electron-impact excitation of He, followed by three-body formation of He ₂ ( a ³ Σ u + ) and Penning ionization of Hg. Emission spectroscopy and kinetic modeling of He/Hg vapor plasmas demonstrate that the population of the Hg ⁺ (6 ² P _1/2 ) radiating state (16.82 eV), produced by direct or two-step electron impact processes, is < 1% of that generated by excitation transfer to Hg by H e 2 * . Flat, fused silica lamps having emitting areas as small as 4 mm ² and containing several mg of ²⁰² Hg and 50–800 Torr of He have been fabricated and serve as optical drivers for the Hg ⁺ atomic clock cycle. Based on small arrays of 500 μ m–1 mm diameter microcavities, these lamps produce peak and average intensities at 194 nm greater than those associated with the Hg resonance transition at ∼ 254 nm, despite the factor of > 3 difference between the energies of the 6 p ³ P ₁ and 6 p ² P _1/2 states of neutral Hg and Hg ⁺ , respectively. These lamps are unique in the sense that the desired radiating species is an excited ion and the background He gas pressure can reach 1 atm, both of which contribute to a dense glow plasma placing severe demands on E / N , power conditioning, and materials selection. Nevertheless, with proper attention given to design, vacuum processing, and preparation of the lamps, lifetimes above 1500 h have been realized to date. When these lamps drive Jet Propulsion Laboratory Hg ⁺ clocks, the stability floor has been measured to be ∼ 10 ⁻¹⁴ . The implications of this lamp for gas-phase and solid-state photochemistry are also discussed.

Cellulose is a glucose polymer and the most abundant biological material on earth. Because it is biodegradable and yet water insoluble, cellulose has been pursued in the past as a scaffold or base structural material for medical applications, sensors, and optical devices. Patterning of two cellulose polymers, cellulose acetate and cellulose acetate butyrate, by photoablative lithography at 172 nm has been demonstrated and is reported here. This 3D subtractive process yields complex micro- and nanostructures and optical components, including sinusoidal gratings and waveguides. Having a depth precision of 15 nm and requiring no photoresist or solvents, vacuum-ultraviolet photoetching of cellulose polymer films proceeds at a constant rate of ∼0.8 μm/h for depths of up to and beyond 25 μm when the intensity of the flat lamp is 10 mW cm⁻². A polydimethylsiloxane (PDMS) microimprinting process, in which photoetched cellulose serves as a negative master mold for PDMS, provides feature sizes as small as 0.5 μm and allows for optical structures such as gratings to be integrated with microfluidic devices while eliminating the existing necessity of fabricating Si molds in a cleanroom environment.