Robert Mamazza

Electrical Properties of Thin-Film Capacitors Fabricated Using High Temperature Sputtered Modified Barium Titanate

Simple thin-film capacitor stacks were fabricated from sputter-deposited doped barium titanate dielectric films with sputtered Pt and/or Ni electrodes and characterized electrically. Here, we report small signal, low frequency capacitance and parallel resistance data measured as a function of applied DC bias, polarization versus applied electric field strength and DC load/unload experiments. These capacitors exhibited significant leakage (in the range 8–210 μA/cm2) and dielectric loss. Measured breakdown strength for the sputtered doped barium titanate films was in the range 200 kV/cm −2 MV/cm. For all devices tested, we observed clear evidence for dielectric saturation at applied electric field strengths above 100 kV/cm: saturated polarization was in the range 8–15 μC/cm2. When cycled under DC conditions, the maximum energy density measured for any of the capacitors tested here was ~4.7 × 10−2 W-h/liter based on the volume of the dielectric material only. This corresponds to a specific energy of ~8 × 10−3 W-h/kg, again calculated on a dielectric-only basis. These results are compared to those reported by other authors and a simple theoretical treatment provided that quantifies the maximum energy that can be stored in these and similar devices as a function of dielectric strength and saturation polarization. Finally, a predictive model is developed to provide guidance on how to tailor the relative permittivities of high-k dielectrics in order to optimize their energy storage capacities.

Sputtered Modified Barium Titanate for Thin-Film Capacitor Applications

New apparatus and a new process for the sputter deposition of modified barium titanate thin-films were developed. Films were deposited at temperatures up to 900 °C from a Ba0.96Ca0.04Ti0.82Zr0.18O3 (BCZTO) target directly onto Si, Ni and Pt surfaces and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Film texture and crystallinity were found to depend on both deposition temperature and substrate: above 600 °C, the as-deposited films consisted of well-facetted crystallites with the cubic perovskite structure. A strongly textured Pt (111) underlayer enhanced the (001) orientation of BCZTO films deposited at 900 °C, 10 mtorr pressure and 10% oxygen in argon. Similar films deposited onto a Pt (111) textured film at 700 °C and directly onto (100) Si wafers showed relatively larger (011) and diminished intensity (00ℓ) diffraction peaks. Sputter ambients containing oxygen caused the Ni underlayers to oxidize even at 700 °C: Raising the process temperature produced more diffraction peaks of NiO with increased intensities. Thin-film capacitors were fabricated using ~500 nm thick BCZTO dielectrics and both Pt and Ni top and bottom electrodes. Small signal capacitance measurements were carried out to determine capacitance and parallel resistance at low frequencies and from these data, the relative permittivity (εr) and resistivity (ρ) of the dielectric films were calculated; values ranged from ~50 to >2,000, and from ~104 to ~1010 Ω∙cm, respectively.

The influence of various front contact materials on the performance of CdTe solar cells

The use of a resistive, or buffer, layer in the front contact structure of CdTe solar cells has been known to improve solar cell performance, in particular when the CdS thickness is relatively small. This paper reviews the performance of CdTe solar cells fabricated on various front contact bi-layer combinations. Conductive (low-/spl rho/) transparent oxides utilized for this work include SnO/sub 2/:F, Cd/sub 2/SnO/sub 4/ and ITO; resistive (high-/spl rho/) transparent oxides include SnO/sub 2/, In/sub 2/O/sub 3/, and Zn/sub 2/SnO/sub 4/. All high-/spl rho/ layers were found to be effective within a range of processing conditions and process/device characteristics. Buffer layers of Zn-Sn-O appear to be the most promising high-/spl rho/ films for the fabrication of CdTe cells with small CdS thickness without compromising the V/sub OC/ and FF.

Characterization of carrier generation and transport mechanisms in single-crystal and thin-film HgI2

Abstract High-electronic-quality thin films of mercuric iodide have been deposited on SnO 2 and other transparent contacts. The crystallites exhibit some preference for c -axis orientation and have lengths comparable to the overall film thickness of 200–400 μm. With visible photons of 584 nm, quantum efficiencies up to 0.5 are observed at an applied voltage of 50 V. amps

Co-sputtered Cd/sub 2/SnO/sub 4/ films as front contacts for CdTe solar cells

Cd/sub 2/SnO/sub 4/ thin films were investigated from a materials point of view as well as from an application point of view through their incorporation into CdTe based solar cells. Cd/sub 2/SnO/sub 4/ was deposited by co-sputtering from CdO and SnO/sub 2/ targets. The lowest resistivity achieved was 2.01/spl times/10/sup -4/ /spl Omega/-cm with a mobility of 29.2 cm/sup 2//V/s and a carrier concentration of 8.47 /spl times/ 10/sup 20/ cm/sup -3/. For this same sample the average transmission was over 90% over the visible and near IR spectrum (400-900nm). When Cd/sub 2/SnO/sub 4/ were used as part of the front contact in thin film CdTe solar cells V/sub oc/s over 840 mV, J/sub sc/s over 23 mA/cm/sup 2/, and ffs over 68.0% were obtained with the best to-date efficiency being 14.0%.

Thin films of CdIn/sub 2/O/sub 4/ as transparent conducting oxides

Cadmium indate, CdIn/sub 2/O/sub 4/, thin films have been deposited on glass substrates by reactive co-sputtering from Cd and In metallic targets in argon ambient with a partial pressure of oxygen of 0.25. The effect of the cadmium-indium ratio on the electro-optical properties of the films was investigated. It was found that films with a Cd/In ratio of 0.37 and subsequent annealing at 600/spl deg/C yielded the best electrical and optical characteristics. Films with such ratios exhibited average optical transmission in the 400-900 nm range of over 90%, with resistivities below 3/spl times/10/sup -4/ /spl Omega/-cm. The lowest resistivity obtained was 2.95/spl times/10/sup -4/ /spl Omega/-cm, corresponding to a mobility of 30.93 cm/sup 2//V/s and carrier concentration of 5.47 /spl times/ 10/sup 20/ cm/sup -3/.