Robert E. Geer

Nanometer-scale mechanical imaging of aluminum damascene interconnect structures in a low-dielectric-constant polymer

Ultrasonic-force microscopy (UFM) has been employed to carry out nanometer-scale mechanical imaging of integrated circuit (IC) test structures comprised of 0.32-μm-wide aluminum interconnect lines inlaid in a low-dielectric-constant (low-k) polymer film. Such inlaid metal interconnects are typically referred to as damascene structures. UFM clearly differentiates the metal and polymer regions within this damascene IC test structure on the basis of elastic modulus with a spatial resolution⩽10 nm. In addition, this technique reveals an increase in the polymer elastic modulus at the metal/polymer interface. This nanometer-scale hardening corresponds to compositional modification of the polymer from the reactive ion etch (RIE) process used to form trenches in the polymer film prior to metal deposition. The reported direct, nondestructive nanometer-scale mechanical imaging of RIE-process-induced modifications of low-k polymers in IC test structures offers expanded opportunities for mechanical metrology and reli...

An ac calorimeter for measuring heat capacity of free‐standing liquid‐crystal films

A unique ac calorimeter for measuring the heat capacity of free‐standing liquid‐crystal films has been developed. A theory of the measurement method used is presented and the experimental setup is discussed. The calorimeter has been used to study the nature of the smectic‐A‐hexatic‐B transition of several liquid‐crystal compounds. The evolution of the heat‐capacity anomaly associated with this transition has been studied for films ranging from three to a few thousand smectic layers in thickness.

Electromechanical robustness of monolayer graphene with extreme bending

We report on the electromechanical robustness of graphene in an extreme condition of deformation: uniaxial bending. A large-angle-bent graphenemonolayer was obtained with a predefined template. Structural/mechanical analysis is conducted, followed by electronic transport measurement. Raman spectroscopy analysis suggests negligible strain in the significantly bent graphene, showing mechanical robustness of the two-dimensional carbon nanostructure. The impact on band structure with respect to key deformation parameters (bending angle and curvature radius) were investigated using sp 3 tight-binding simulation. Results show insignificant local band modification at bending locations. Even with extreme deformation, excellent carrier mobility in monolayergraphene is preserved.

Quantitative nanoscale modulus measurements and elastic imaging of SnO2 nanobelts

A comparative study of the elastic modulus and uniformity of single-crystal SnO2 nanobelts is presented employing two nondestructive techniques based on atomic force microscopy: differential ultrasonic force microscopy (d-UFM) and atomic force acoustic microcopy (AFAM). In mapping mode both techniques revealed a uniform elastic response across the surface of the nanobelts as expected for single-crystal nanostructures. Comparative analyses of the local indentation modulus (probe area≈100–400nm2) were undertaken using both techniques at multiple points on the same SnO2 nanobelt exhibiting a (102) surface crystalline orientation as determined by electron backscatter diffraction. Both d-UFM and AFAM exhibited excellent quantitative agreement yielding indentation moduli of 151±14 and 154±18GPa, respectively. These values are significantly below the expected value of the (102) indentation modulus of 358GPa for crystalline SnO2 determined from the Green’s function model of Barnett and Lothe [Phys. Nors. 8, 13 (1...

Controlling uniformity of RRAM characteristics through the forming process

The proposed constant voltage forming (CVF) is shown to increase the resistances of the low resistance and high resistance states while reducing their variability. By forcing the forming in all devices to occur at the same predefined voltage, the CVF method eliminates a major cause of the device-to-device variation associated with the randomness of the forming voltage values. Moreover, both experiments and simulations show that CVF at lower voltages suppresses the parasitic overshoot current, resulting in a more controlled and smaller filament cross-section and lower operation currents.

Superior TID Hardness in TiN/HfO

Resistive switching properties of valence change memory (VCM) resistive-random-access-memory (ReRAM) devices (TiN/HfO2 /TiN) are investigated after exposure to proton radiation with total ionizing doses (TID) of 1.5, 3, and 5 Grad(Si) and compared to similar measurements from electrochemical metallization memory (ECM) ReRAM devices (Pt/HfO2:Cu/Cu). The TiN/HfO2/TiN ReRAMs show significantly superior TID radiation-hardness compared to Pt/HfO2:Cu/Cu ReRAMs: 1) All devices remained functional after radiation; 2) switching parameters including average Vset, Vreset, Ron, Roff showed minimal or no degradation; and 3) TID radiation enhanced the uniformity of resistive switching among all VCM devices. The superior radiation responses of the VCM ReRAM devices relative to ECM ReRAMs result from the distinct conduction filament (CF) formation mechanisms. For the VCM ReRAM system, the radiation-induced vacancy density does not serve to inhibit the trap-assisted tunneling associated with the Hf-rich CF formation kinetics. On the contrary, vacancy-promoted charge trapping promotes VCM CF stability. In strong contrast, proton-induced vacancies for the ECM ReRAMs inhibit the formation of the metallic filament through internal field reduction due to charge trapping. The comparison of TID effects suggests that HfO2-based VCM ReRAMs can be made radiation immune to a TID up to 5 Grad(Si) and may be highly suitable for rad-hard electronics applications.

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In this paper, radio frequency (RF) through-silicon via (TSV) designs and models are proposed to achieve high-frequency vertical connectivity for three dimensional (3D) multi-core and heterogeneous ICs. Specifically, coaxial dielectric and novel air-gap-based TSVs are designed and simulated to reduce signal degradation during RF operations. The simulation results demonstrate that these RF TSVs can provide decay-tolerance frequencies two orders of magnitude higher than simple Cu-plug TSVs. The data rate and energy per bit of the RF TSVs are summarized, providing an important guideline for future 3D high-frequency TSV designs.

/TiN ReRAMs After Proton Radiation

A quantitative study of the effect of electric field on the stripe domains formed by layer deformation in chiral smectic A liquid crystals is presented. X‐ray diffraction studies reveal that the angle between the layer normals in adjacent stripe domains increases with increasing electric field. A simple model is presented to derive the true molecular tilt angle from optical transmission measurements. The relationship between the optical tilt angle and the tilt angle evaluated from x‐ray measurements of the smectic layer thickness indicates that the molecules are tilting as rigid rods.

Electrical characterization of RF TSV for 3D multi-core and heterogeneous ICs

The electronic structure and transport properties of silver (Ag) and copper (Cu) nanowires of diameters up to 1.7 nm are investigated using first principles density functional theory and the Landauer formalism in conjunction with a supercell approach. A direct comparison of the ballistic conductances, quantum capacitances, and kinetic inductances indicates that Ag and Cu nanowires show very similar performances. Compared to the electrostatic capacitance, the quantum capacitance is found to have a negligible effect on the total capacitance of the nanowire interconnect. In contrast, the overall inductance has a dominant contribution from the kinetic inductance over the magnetic inductance.

Influence of the electric field on the quasibookshelf stripe deformation in an electroclinic liquid crystal

Simulations of the dynamic physical processes involved in HfO2-based resistive-memory-operations are used to identify the dielectric structural properties responsible for device performance, while revealing that repeatable switching and higher HRS resistances are enabled by the oxide sub-stoichiometric composition. These simulations support a conductive-filament-formation physical model which is resulted from metal-oxygen bond breakage and subsequent oxygen ion out-diffusion, thus leaving behind an oxygen-vacancy rich region. The subsequent reset process is also shown to be controlled by re-oxidation of the filament tip.