M.K. Hota

Graphene oxide-based flexible metal–insulator–metal capacitors

This work explores the fabrication of graphene oxide (GO)-based metal–insulator–metal (MIM) capacitors on flexible polyethylene terephthalate (PET) substrates. Electrical properties are studied in detail. A high capacitance density of ~4 fF µm−2 measured at 1 MHz and permittivity of ~6 have been obtained. A low voltage coefficient of capacitance, VCC-α, and a low dielectric loss tangent indicate the potential of GO-based MIM capacitors for RF applications. The constant voltage stressing study has shown a high reliability against degradation up to a projected period of 10 years. Degradation in capacitance of the devices on flexible substrates has been studied by bending radius down to 1 cm even up to 6000 times of repeated bending.

Charge trapping and reliability characteristics of sputtered Y2O3 high-k dielectrics on N- and S-passivated germanium

We demonstrate the potential of sulfur passivation to improve the interface characteristics between germanium (Ge) and Y2O3 high-k gate dielectric. Effects of nitrogen (N) and sulfur (S) passivation of the Ge surface on the charge trapping and reliability properties of Y2O3/Ge gate stacks are studied in detail and the results are compared. Sulfur passivation of the Ge surface has been performed using both the wet sulfidation technique with aqueous ammonium sulfide and plasma sulfidation with H2S gas. N-passivation of Ge substrates has been performed in NO plasma for comparison. Ultrathin (~15 nm) Y2O3 films are deposited on both the N- and S-passivated p-Ge (1 0 0) wafers. Y2O3 films on the S-passivated Ge surface show low fixed oxide charge and interface state density than what is achieved with N-passivation. The electrical characterization results of MOS capacitors with Y2O3 films reveal the potential of S-passivation for the fabrication of Y2O3/Ge gate stacks for Ge MOSFETs.

Structural and Electrical Properties of Radio Frequency Sputtered HfTaOx Films for High-k Gate Insulator

Mixed HfTaOx dielectric has been deposited by radio frequency (RF) magnetron co-sputtering of HfO2 and Ta2O5 targets on Si substrates and with Pt bottom electrode for metal–oxide–semiconductor (MOS) and metal–insulator–metal (MIM) structures, respectively. HfTaOx layers are characterized by X-ray photoelectron spectroscopy (XPS) to examine the chemical composition. Surface morphology and crystallinity of the deposited film were examined, using by atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD), respectively. For both the structures electrical properties have been studied in detail. MOS capacitor capacitance–voltage (C–V) characteristics have been utilized to determine the interface trap density and trap distribution in the silicon band gap. A small capacitance non-linearity and low dissipation factor were found in the Pt/HfTaOx/Pt MIM structures.

Paramagnetic defects and charge trapping in TaYOx gate dielectrics on strained-Si

Charge trapping kinetics and chemical nature of defects present in Al/TaYOx/strained-Si/Si0.8Ge0.2 MIS capacitors have been studied using internal photoemission and magnetic resonance. Reliability characteristics have been studied using CVS and CCS techniques. Results of electron paramagnetic resonance (EPR) and internal photoemission (IPE) studies on the charge trapping behavior are reported.

Temperature dependence of TaAlOx metal-insulator-metal capacitors

Structural and electrical properties of amorphous tantalum aluminum oxide (TaAlOx) films deposited using rf magnetron sputtering are investigated using metal-insulator-metal (MIM) capacitor structures with Au as metal electrodes. Crystallinity of the deposited films was studied using grazing incidence x-ray diffraction analysis. The frequency dependence of temperature coefficient of capacitance, an important parameter for precision MIM capacitors, is studied using the Au/TaAlOx/Au stacked layer. The effects of annealing temperature and the ambient on the physical and electrical properties of TaAlOx-based high-k MIM capacitors are reported. Low nonlinearity in capacitance values was found for samples annealed in O2 ambient. Dielectric loss and permittivity are found to increase with increase in temperature.

Reliability behavior of TaAlOx Metal-Insulator-Metal capacitors

Reliability characteristics of TaAlO<inf>x</inf> high-k dielectric MIM capacitors are reported. TaAlO<inf>x</inf> films have been deposited by RF co-sputtering of Ta<inf>2</inf>O<inf>5</inf> and Al<inf>2</inf>O<inf>3</inf> targets at a low substrate temperature. A high capacitance density and a low value of VCC (voltage coefficients of capacitance) have been achieved. Degradation kinetics in TaAlO<inf>x</inf>-based MIM capacitors have been studied under constant current stressing (CCS: 20 to 60 nA) and constant voltage stressing (CVS: 3 to 7 V). A dielectric breakdown voltage in the range of ∼ 4.2 – 5.4 MV/cm was found for TaAlO<inf>x</inf> films.

Characterization of RF sputter deposited HfAlOx dielectrics for MIM capacitor applications

Advanced metal-insulator-metal (MIM) capacitors with ultra-thin (EOT~2.1-4.9nm) RF sputter-deposited HfAlOx dielectric layers having excellent electrical properties have been fabricated. The capacitance density is found to increase with the decrease in thickness of insulator film. MIM capacitors show little voltage and frequency dependence along with low dissipation and leakage current. Our experimental observations indicate the high potential of HfAlOx for MIM capacitor applications.

Effects of constant voltage stressing on HfTaOx/SiGe gate stack

Ultrathin HfTaOx gate dielectric has been deposited on Si0.81Ge0.19 by RF co-sputtering of HfO2 and Ta2O5 targets. X-ray photoelectron spectroscopic (XPS) analyses indicate an interfacial layer containing GeOx, Hf silicate, SiOx (layer of Hf- Si-Ge-O) formation during deposition of HfTaOx. No evidence of Ta-silicate or Ta incorporation was found at the interface. X-ray diffraction (GIXRD) measurements show that as-deposited HfTaOx films are amorphous; however, the crystallization temperature of HfTaOx film is found to increase significantly after annealing beyond 500 °C (for 5 min) along with the incorporation of Ta (with 18% Ta). It has been found that HfTaOx gate dielectric on Si0.81Ge0.19 exhibit excellent electrical properties with low interface state density (~6.0×1011 cm-2eV-1) and hysteresis voltage (<70 mV). Charge trapping/detrapping behavior of the gate stacks has been studied under constant voltage stressing and the degradation mechanism of the dielectrics has been studied in detail.

Studies on Lattice vibration, impurity and defects in MIS structures using Hf-based dielectrics on Si and SiGe substrates

Lattice dynamics, molecular vibrations as well as defects and traps in ultra-thin Hf-based gate dielectrics on Si and strained-SiGe layers have been studied using inelastic tunneling spectroscopy (IETS). Molecular vibrations, phonons, defects and trap-features are identified from IETS of the samples for comparing and analyzing different interface qualities.

Effects of metal nanodots (Au and Pd) on Nb2O5 memristors

The memristive behavior has been observed with Au and Pd metal nanodots embedded high-k dielectric films of Nb2O5. A superior control in terms of consistency during transition between two resistances states have been found for Pd embedded Nb2O5 devices as a consequence of better control of formation or rupture of conductive filaments. Direct surveillance of the formation or rupture of conductive filaments at nanoscale during memristive switching are performed using current imaging tunneling spectroscopy (CITS) technique as measured by scanning tunneling microscope.