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10 May 1993

Volume 62, Issue 19, pp. 2301-2447

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High‐speed InP/InGaAs double‐heterostructure bipolar transistors with suppressed collector current blocking

K. Kurishima, H. Nakajima, T. Kobayashi, Y. Matsuoka, and T. Ishibashi

Appl. Phys. Lett. 62, 2372 (1993); http://dx.doi.org/10.1063/1.109368 (3 pages) | Cited 9 times

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InP/InGaAs double‐heterostructure bipolar transistors (DHBTs), incorporating a new collector structure featuring ‘‘pn pair doping’’ in the heterointerface vicinity, have been fabricated using a low‐pressure metalorganic chemical vapor deposition (MOCVD) method. These transistors provide high collector current densities over 1×105 A/cm2, indicating the successful suppression of current blocking. S‐parameter measurements determine the high current gain cutoff frequencies of 130 GHz. These values favorably compare with those of conventional InGaAs‐collector HBTs fabricated for comparison, suggesting that the InP collectors have excellent electron transport properties.  
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85.30.Pq Bipolar transistors
85.30.De Semiconductor-device characterization, design, and modeling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

High‐resolution x‐ray diffraction to determine the self‐limiting growth in atomic layer epitaxy of InP and InAs/InP heterostructures

C. A. Tran, R. A. Masut, J. L. Brebner, and R. Leonelli

Appl. Phys. Lett. 62, 2375 (1993); http://dx.doi.org/10.1063/1.109369 (3 pages) | Cited 7 times

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High‐resolution x‐ray diffraction (HRXRD) can be used to quickly and precisely evaluate the self‐limiting growth of atomic layer epitaxy (ALE) of III‐V compounds and heterostructures. We have studied atomic layer epitaxy of InP and InAs/InP heterostructures in a conventional low pressure metalorganic vapor phase epitaxy reactor. We used the interference of x‐ray wave fields in the grown structures to measure nondestructively the thickness of the deposited film with relatively high precision. A self‐limiting growth close to 1 monolayer/cycle has been obtained for InP and InAs with a substrate temperature as low as 350–360 °C. HRXRD and photoluminescence measurements have demonstrated the structural and optical high quality of ALE‐grown InP and InAs/InP heterostructures.
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68.55.-a Thin film structure and morphology
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Atomic layer epitaxy of GaAs with a 2 μm/h growth rate

Anthony Dip, Gamal M. Eldallal, Peter C. Colter, N. Hayafuji, and S. M. Bedair

Appl. Phys. Lett. 62, 2378 (1993); http://dx.doi.org/10.1063/1.109370 (3 pages) | Cited 6 times

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Atomic layer epitaxy (ALE) of GaAs with a growth rate as high as 2 μm/h was achieved in a specially designed reactor based on the rotating susceptor concept. High deposition rates are made possible by a unique partition system that permits rapid rotation of substrates between simultaneous streams of columns III and V reactant gases. Mixing of the gas streams at high rotational speeds is avoided by the gas shearing effect provided by the partition system. Background carbon levels in the GaAs films with high growth rates varied from mid 1017 cm−3 at 650 °C to mid 1018 cm−3 at 550 °C. When the growth rate was reduced to 0.3 μm/h, carbon background doping in the 1015 cm−3 was achieved.
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68.55.-a Thin film structure and morphology

Time resolved photoluminescence of porous silicon: Evidence for tunneling limited recombination in a band of localized states

L. R. Tessler, F. Alvarez, and O. Teschke

Appl. Phys. Lett. 62, 2381 (1993); http://dx.doi.org/10.1063/1.109371 (3 pages) | Cited 37 times

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Time resolved photoluminescence of porous silicon at room temperature was measured for several emission energies under 2 ns nitrogen laser excitation. For each emission energy studied there is a broad distribution of lifetimes extending over a few decades. The mean value of the distribution varies with the emission energy, from 3 (2.77 eV) to 50 μs (1.96 eV). The results can be explained by assuming a tunneling limited recombination mechanism between bands of localized states. We associate this behavior with a superficial disordered Si:O:H compound rather than with quantum confinement effects.
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78.55.Hx Other solid inorganic materials
71.23.An Theories and models; localized states

Enhancement of photosensitivity by ultraviolet irradiation and photoconductivity spectra of diamond thin films

R. Vaitkus, T. Inushima, and S. Yamazaki

Appl. Phys. Lett. 62, 2384 (1993); http://dx.doi.org/10.1063/1.109372 (3 pages) | Cited 24 times

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The evolution of photocurrent in time under ultraviolet (UV) irradiation of free‐standing diamond thin films, prepared by chemical vapor deposition method, have been observed. A significant enhancement of the photosensitivity in visible‐near‐infrared region of UV illuminated samples have been obtained. The linear dependence of relative change of photocurrent on UV radiant intensity have been found. The photoconductivity spectra have been investigated in the energy range 1–6.2 eV. The results of investigation have shown that diamond thin films possess similar properties as radiation damaged crystalline diamond.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Db Elemental semiconductors and insulators

Optical characterization of pure ZnSe films grown on GaAs

Young‐Dong Kim, S. L. Cooper, M. V. Klein, and B. T. Jonker

Appl. Phys. Lett. 62, 2387 (1993); http://dx.doi.org/10.1063/1.109373 (3 pages) | Cited 40 times

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We report the first spectroscopic ellipsometry study of the E0, E0+Δ0, E1, and E1+Δ1 critical points in high‐quality ZnSe films. These data seem to be the best identification of E1 and E1+Δ1 peaks to date using ellipsometry. We also describe a chemical etching procedure which was successfully used to remove the natural surface oxide overlayer on the ZnSe films. X‐ray photoelectron spectroscopy data after NH4OH treatment shows the disappearance of oxygen and oxidized Se peaks demonstrating the successful removal of surface oxide overlayer on ZnSe.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
81.65.-b Surface treatments

High‐power InGaN/GaN double‐heterostructure violet light emitting diodes

Shuji Nakamura, Masayuki Senoh, and Takashi Mukai

Appl. Phys. Lett. 62, 2390 (1993); http://dx.doi.org/10.1063/1.109374 (3 pages) | Cited 250 times

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InGaN/GaN double‐heterostructure light‐emitting diodes were fabricated. The output power was 90 μW and the external quantum efficiency was as high as 0.15% at a forward current of 20 mA at room temperature. The peak wavelengths of the electroluminescence (EL) varied between 411 and 420 nm with changes in the growth temperatures of an InGaN active layer between 820 and 800 °C. The full widths at half maximum of EL were between 22 and 25 nm.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Blocking of Γ→X transfer in GaAs/AlAs short period superlattices due to X‐state band filling

P. W. M. Blom, C. Smit, J. E. M. Haverkort, and J. H. Wolter

Appl. Phys. Lett. 62, 2393 (1993); http://dx.doi.org/10.1063/1.109375 (3 pages) | Cited 5 times

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We report an experimental study of the optical properties of a GaAs/AlAs short period superlattice (SPSL) by photoluminescence and time‐resolved two‐pulse correlation experiments. Our SPSL is designed in such a way that the lowest confined Γ state in the GaAs is only slight (30–50 meV) above the X states in the AlAs. Therefore the Γ→X transfer due to LO‐phonon emission or interface scattering is prohibited by X‐band filling at high excitation densities and small excess energies, which allows us to measure a Γ→X transfer time induced by LO‐phonon absorption of 20 ps. By adjusting the laser energy, excitation density, and temperature we are able to transform the emission spectrum of the SPSL completely from a type‐I into a type‐II transition.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Surface‐enhanced Raman scattering of amorphous silicon‐carbon films

M. B. Tzolov, N. V. Tzenov, D. I. Dimova‐Malinovska, and D. Y. Yankov

Appl. Phys. Lett. 62, 2396 (1993); http://dx.doi.org/10.1063/1.109376 (3 pages) | Cited 7 times

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Surface‐enhanced Raman scattering has been used to study the surface of magnetron sputtered amorphous silicon‐carbon alloys applying the silver overlayer method. The presence of clusters from the sputtered material and different types of carbon–carbon bond configurations has been detected on the film surface. It has been shown that structural transformations which are not related to the hydrogen in the plasma take place on the surface.
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78.30.Hv Other nonmetallic inorganics
68.35.B- Structure of clean surfaces (and surface reconstruction)
63.50.-x Vibrational states in disordered systems
81.15.Cd Deposition by sputtering

Molecular beam epitaxy of strained PbTe/EuTe superlattices

G. Springholz and G. Bauer

Appl. Phys. Lett. 62, 2399 (1993); http://dx.doi.org/10.1063/1.109377 (3 pages) | Cited 20 times

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Using reflection high energy electron diffraction (RHEED), the phase diagram of strained layer heteroepitaxy of EuTe by molecular beam epitaxy on PbTe(111) surfaces was determined. The EuTe(111) surface exhibits different surface reconstructions corresponding to a Te‐stabilized or an Eu‐stabilized surface state. For perfect two‐dimensional layer‐by‐layer heteroepitaxial growth, only a narrow process window exists which can be determined by RHEED. Using such established growth conditions, we have fabricated strained PbTe/EuTe superlattices with superior structural perfection as shown by high resolution x‐ray diffraction.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

High temperature characteristics of InGaAsP/InP laser structures

H. Temkin, D. Coblentz, R. A. Logan, J. P. van der Ziel, T. Tanbun‐Ek, R. D. Yadvish, and A. M. Sergent

Appl. Phys. Lett. 62, 2402 (1993); http://dx.doi.org/10.1063/1.109378 (3 pages) | Cited 47 times

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We investigate the high temperature performance of conventional separate confinement and lattice matched and compressively strained multi‐quantum‐well InGaAsP lasers emitting at 1.3 μm. Low threshold buried heterostructure lasers operate reproducibly at temperatures as high as 130 °C. The rate of threshold change with temperature is described by T0∼45°–55° for both conventional and quantum well lasers. The rate of change is not influenced by any modifications in the active layer structure. In contrast, excellent correlation is observed between the active layer structure, parametrized as the threshold gain, and the peak cw operating temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Observation of a delocalized E′ center in buried SiO2

K. Vanheusden and A. Stesmans

Appl. Phys. Lett. 62, 2405 (1993); http://dx.doi.org/10.1063/1.109379 (3 pages) | Cited 15 times

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The oxygen‐vacancy defect (E′) generated at the surface of buried SiO2 (BOX) layers of the separation by implantation of oxygen structure has been studied by K‐band electron spin resonance. Besides the usual Eγ′ signal, the Eδ′ center—a delocalized variant of the E′ center—has been identified in the BOX. No such signal, however, was observed in reoxidized (950 °C; 1.1 atm O2) BOX or conventional thermal oxide. These data lead to the proposal of an adapted model for the defect, based on the existence of small Si clusters (≳5 atoms) in the BOX serving as E′ defect precursors. This model implies that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.  
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.uf Ge and Si
68.35.Dv Composition, segregation; defects and impurities

Further evidence for quantum confinement in porous silicon

R. Behrensmeier, Fereydoon Namavar, G. B. Amisola, F. A. Otter, and J. M. Galligan

Appl. Phys. Lett. 62, 2408 (1993); http://dx.doi.org/10.1063/1.109380 (3 pages) | Cited 20 times

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The origin of the photoluminescence (PL) of porous silicon is being extensively investigated. In this letter, we offer detailed analyses of the PL spectra, of which about 3%–5% show small extrema that superimpose the larger main peak. Spacing between these smaller maxima is reproducible and independent of the main peak energy and sample history, while energy steps between them correlate with differences in the exciton energies due to changing the sizes of the quantum wires by complete monolayers of atoms.
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78.55.Hx Other solid inorganic materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Direct determination of the ambipolar diffusion length in strained InxGa1−xAs/InP quantum wells by cathodoluminescence

Robert B. Lee, Kerry J. Vahala, Chung‐En Zah, and Rajaram Bhat

Appl. Phys. Lett. 62, 2411 (1993); http://dx.doi.org/10.1063/1.109381 (2 pages) | Cited 4 times

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The ambipolar diffusion length is measured in strained InxGa1−xAs/InP quantum wells for several mole fractions in the interval 0.3<x<0.8 by cathodoluminescence. The ambipolar diffusion length is found to have a significantly higher value in the lower indium mole fraction samples corresponding to tensile‐strained wells. This longer diffusion length for the tensile samples is consistent with results of carrier lifetime experiments by M. C. Wang, K. Kash, C. E. Zah, R. Bhat, and S. L. Chuang [Appl. Phys. Lett. 62, 166 (1993)].
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.60.Hk Cathodoluminescence, ionoluminescence

Strain effects in the intersubband transitions of narrow InGaAs quantum wells

L. H. Peng, J. H. Smet, T. P. E. Broekaert, and C. G. Fonstad

Appl. Phys. Lett. 62, 2413 (1993); http://dx.doi.org/10.1063/1.109382 (3 pages) | Cited 13 times

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Internal uniaxial stress effects on the degenerate P‐like C2 subband Bloch states of Si‐doped (001) InGaAs single quantum wells (SQWs) have been studied using polarization‐resolved infrared spectroscopy. It is found that a tetragonal strain perturbation of the crystal potential produces a splitting between the TM and TE active intersubband transitions. The magnitude of the linear strain intersubband deformation potential of InGaAs quantum wells is 3 eV.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

In‐plane effective mass in narrow quantum wells of nonparabolic semiconductors

B. R. Nag and Sanghamitra Mukhopadhyay

Appl. Phys. Lett. 62, 2416 (1993); http://dx.doi.org/10.1063/1.109633 (3 pages) | Cited 13 times

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A formula is derived for the in‐plane effective mass in narrow quantum wells, taking into account the effects of energy band nonparabolicity. The variation of the mass with the width of the well is studied by using the formula for four systems of wells. The mass is nearly the same as the velocity effective mass of the bulk material of the well in GaAs/Ga0.7Al0.3As wells. It is about 8% larger in InAs/InP wells, but is significantly larger in very narrow wells of Ga0.47In0.53As/InP systems. In the case of InAs/Ga0.58Al0.42Sb wells, the in‐plane mass differs from the well mass by large amounts for all well widths of interest.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Penetration depth λ(T) of YBa2Cu3O7−δ films determined from the kinetic inductance

JuYoung Lee and Thomas R. Lemberger

Appl. Phys. Lett. 62, 2419 (1993); http://dx.doi.org/10.1063/1.109383 (3 pages) | Cited 19 times

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We examine the temperature dependence of the magnetic penetration depth λ(T) of YBa2Cu3O7−δ, determined from the kinetic inductance of a film patterned into a long meander line. This technique has sufficient sensitivity to study λ(T) to lower temperatures than have been examined previously. A numerical model which includes both the magnetic and kinetic inductances of the samples extracts λ(T) from the measured voltage. In reasonable agreement with other measurements, λ(0)≊2100 Å is deduced from fitting λ(0)2/λ(T)2 to the function 1−(T/Tc)2 for T/Tc≥0.4. We find λ(T)/λ(0)−1 is proportional to (T/Tc)2 for 0.06 ≤T/Tc≤0.4.
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74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

In situ, rf plasma deposition of Bi2Sr2Ca2Cu3Ox thin films at atmospheric pressure

A. Shah, S. Patel, E. Narumi, and D. T. Shaw

Appl. Phys. Lett. 62, 2422 (1993); http://dx.doi.org/10.1063/1.109384 (3 pages) | Cited 2 times

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Superconducting Bi2Sr2Ca2Cu3Ox thin films have been prepared in situ at atmospheric pressure by an inductively coupled, argon‐oxygen rf plasma. This high Tc phase has been achieved by exposing the grown film, in situ, to the same argon‐oxygen plasma used for the deposition of the film. No post‐annealing steps are required. Bi2Sr2Ca2Cu3Ox films with critical temperatures of 100 K and critical current densities of 1×105 A/cm2 at 77 K and zero field have been obtained at a deposition rate of 100–200 Å/min. The films are mirror smooth with very few particulates and pinholes. Control of the substrate heater temperature is critical as high‐quality films grow only in a narrow temperature range. The effect of plasma treatment and substrate heater temperature is discussed.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Superconducting Y1Ba2Cu3O7−x/Nd1.85Ce0.15CuO4−y bilayer thin films

S. N. Mao, X. X. Xi, Qi Li, I. Takeuchi, S. Bhattacharya, C. Kwon, C. Doughty, A. Walkenhorst, T. Venkatesan, C. B. Whan, J. L. Peng, and R. L. Greene

Appl. Phys. Lett. 62, 2425 (1993); http://dx.doi.org/10.1063/1.109385 (3 pages) | Cited 14 times

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Bilayers of Y1Ba2Cu3O7−x(YBCO)/Nd1.85Ce0.15CuO4−y(NCCO), in which both layers were superconducting, were fabricated in situ by pulsed laser deposition. Using N2O as the reactive gas, we were able to meet the conflicting processing requirements, oxygenation for YBCO, and reduction for NCCO, in the same sample with a specific cooling procedure. The bilayer thin films were c‐axis oriented with a transition temperature, Tco, of 88.5 K for YBCO and 18.5 K for NCCO. Supercurrent was observed across the interface of the YBCO and NCCO superconducting layers, indicating the phase coherence between these superconductors.
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81.15.Fg Pulsed laser ablation deposition
74.78.-w Superconducting films and low-dimensional structures
74.78.Fk Multilayers, superlattices, heterostructures

Epitaxial YBa2Cu3O7−y bolometers on micromachined windows in silicon wafers

Q. Li, D. B. Fenner, W. D. Hamblen, and D. G. Hamblen

Appl. Phys. Lett. 62, 2428 (1993); http://dx.doi.org/10.1063/1.109386 (3 pages) | Cited 24 times

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Epitaxial YBCO thin‐film bolometers have been successfully fabricated on thin Si(100) substrates. Substrates included prethinned wafers ranging from 400 μm down to 4 μm thick, and a window, 0.75 μm thick, micromachined into a 400‐μm wafer. As the Si is made thinner, the speed and responsivity both improve considerably. A 500‐μs rise time was achieved on the micromachined window bolometer (0.75‐μm‐thick Si) under chopped infrared illumination. Calculations of heat flow in Si windows are in excellent agreement with the observed window‐bolometer response waveform.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
74.25.N- Response to electromagnetic fields
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Limitations of magnetoresistive sensors based on the giant magnetoresistive effect in granular magnetic composites

T. L. Hylton

Appl. Phys. Lett. 62, 2431 (1993); http://dx.doi.org/10.1063/1.109387 (3 pages) | Cited 13 times

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The giant magnetoresistive effect recently observed in thin film composites of ferromagnetic particles imbedded in a nonmagnetic metallic matrix offers the possibility that new magnetoresistive sensors can be fabricated using these structures. Here we consider the effects of particle size and shape, magnetocrystalline anisotropy and temperature on the performance and sensitivity of such devices. For the sensitivity required in read elements of high‐performance magnetic heads, severe constraints on the choice of ferromagnetic material and particle size and shape are required.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Properties of epitaxial SrRuO3 thin films

X. D. Wu, S. R. Foltyn, R. C. Dye, Y. Coulter, and R. E. Muenchausen

Appl. Phys. Lett. 62, 2434 (1993); http://dx.doi.org/10.1063/1.109388 (3 pages) | Cited 88 times

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SrRuO3 thin films were deposited on (100) LaAlO3 using pulsed laser deposition. The films were (001) oriented normal to the substrate surface with a high degree of in‐plane orientation with respect to the substrate’s major axes. An ion beam minimum yield of 2.5% was obtained for the films, indicating high crystallinity. The films exhibited metallic behavior with a room temperature resistivity of ∼200 mW cm. A kink in the resistivity, corresponding to a ferromagnetic phase transition, was observed at ∼160 K. It was found that SrRuO3 is structurally and chemically compatible with the YaB2Cu3O7−d (YBCO) superconductors. High quality YBCO films were obtained on SrRuO3 LaAlO3. Multilayers of YBCO/SrRuO3 were successfully fabricated.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
74.78.Fk Multilayers, superlattices, heterostructures
74.78.-w Superconducting films and low-dimensional structures

Al2O3+x/Al interface formation by promoted oxidation using an alkali metal and removal of the catalyst

Y. Huttel, E. Bourdié, P. Soukiassian, P. S. Mangat, and Z. Hurych

Appl. Phys. Lett. 62, 2437 (1993); http://dx.doi.org/10.1063/1.109364 (3 pages) | Cited 6 times

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We report the effect of Na overlayers on the oxidation of Al thin films by core level photoemission spectroscopy using synchrotron radiation. The presence of a Na monolayer enhances the aluminum room temperature oxidation rate by 4 orders of magnitude with formation of alumina as Al2O3 and Na oxides, possibly as aluminates. Furthermore, the Na catalyst could be desorbed from the surface by a rapid thermal annealing at temperatures below 300 °C, leading to the growth of aluminum oxides having a binding energy larger than stoichiometric Al2O3. It indicates the formation at the surface of Al oxides having higher oxidation states.
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81.65.-b Surface treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Tactile shear sensing using anisotropically conductive polymer

L. H. Chen, S. Jin, and T. H. Tiefel

Appl. Phys. Lett. 62, 2440 (1993); http://dx.doi.org/10.1063/1.109365 (3 pages) | Cited 3 times

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A new technique for tactile shear sensing using a z‐direction‐only conductive polymer material is discussed. A thin layer of the material is in situ cured, in the presence of a z‐direction magnetic field, on the surface of a circuit board containing a contact‐pad array. A small metallic cursor embedded in an overlaid elastomeric skin slides over the z‐direction conductive polymer upon shear motion, and its change in position is detected by the occurrence of simple circuit connections between neighboring contact pads. This shear sensor has the advantages of being compliant, transparent, able to accommodate pad height variations, and capable of high‐resolution sensing. It may also serve as temperature and pressure sensor because of the characteristic and reversible variation of the z‐direction electrical resistance in the conductive polymer upon changes in ambient temperature and contact pressure. The new sensor may be useful for potential applications such as touch‐sensitive controllers for computer‐related products and robotic skins.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.Qk Reinforced polymers and polymer-based composites
81.40.Rs Electrical and magnetic properties related to treatment conditions

Effect of interface layer on the microstructure and electromigration resistance of Al‐Si‐Cu alloy on TiN/Ti substrates

J. O. Olowolafe, H. Kawasaki, C. C. Lee, J. Klein, F. Pintchovski, and D. Jawarani

Appl. Phys. Lett. 62, 2443 (1993); http://dx.doi.org/10.1063/1.109366 (3 pages) | Cited 4 times

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Al‐Si‐Cu alloy films sputter‐deposited on reactively ion‐sputtered TiN/Ti/SiO2 substrates were characterized and evaluated for interconnect reliability. Using x‐ray diffraction techniques, both TiN and Al microstructures were analyzed and the (111) intensities of the latter correlated with the electromigration median time to fail (MTTF). The values of the MTTF increased with the Al(111) intensities for the TiN/Ti/SiO2 substrates annealed below 400 °C. A progressive decrease in both the Al(111) texture and MTTF was observed for substrates annealed above this temperature. While the improved Al(111) texture has been attributed to an improved TiN barrier textured in the (111) crystal plane (anneals below 400 °C), a TiO2 layer over the TiN barrier has been found responsible for the degradation of the Al(111) texture and the MTTF for barrier anneals above 400 °C.
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66.30.Qa Electromigration
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
85.40.Ls Metallization, contacts, interconnects; device isolation
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