Wide-band-gap oxides such as SrTiO3 are shown to be critical tests of theories of Schottky barrier heights based on metal-induced gap states and charge neutrality levels. This theory is reviewed and used to calculate the Schottky barrier heights and band offsets for many important high dielectric constant oxides on Pt and Si. Good agreement with experiment is found for barrier heights. The band offsets for electrons on Si are found to be small for many key oxides such as SrTiO3 and Ta2O5 which limit their utility as gate oxides in future silicon field effect transistors. The calculations are extended to screen other proposed oxides such as BaZrO3. ZrO2, HfO2, La2O3, Y2O3, HfSiO4, and ZrSiO4. Predictions are also given for barrier heights of the ferroelectric oxides Pb1−xZrxTiO3 and SrBi2Ta2O9 which are used in nonvolatile memories.

Band offsets of wide-band-gap oxides and implications for future electronic devices

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

An architectural rationale and an experimental program aimed at the development of molecular electronics switching devices for memory and computing applications are discussed. Two-terminal molecular switch tunnel junctions are identified as the critical device components of molecular electronics-based circuitry. They can be tiled in two dimensions and are tolerant of manufacturing defects. Singly and multiply configurable solid-state switching devices that are based upon electrochemically switchable molecular and supramolecular systems are discussed in terms of both the synthesis of the molecular components and the fabrication and performance of the devices.

Switching devices based on interlocked molecules.

A molecular wire crossbar memory (MWCM) system is provided. The MWCM comprises a two-dimensional array of a plurality of nanometer-scale devices, each device comprising a junction formed by a pair of crossed wires where one wire crosses another and at least one connector species connecting the pair of crossed wires in the junction. The connector species comprises a bi-stable molecular switch. The junction forms either a resistor or a diode or an asymmetric non-linear resistor. The junction has a state that is capable of being altered by application of a first voltage and sensed by application of a second, non-destructive voltage.

Molecular wire crossbar memory

Addressing an array of bistable [2]rotaxanes through a two-dimensional crossbar arrangement provides the device element of a current-driven molecular electronic circuit. The development of the [2]rotaxane switches through an iterative, evolutionary process is described. The arrangement reported here allows both memory and logic functions to use the same elements.

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Two-dimensional molecular electronics circuits.

Ferroelectric non-volatile memories for low-voltage, low-power applications

Time‐zero current‐voltage characteristics and time‐dependent current behavior of metal‐ferroelectric‐metal (Pt‐PZT‐Pt) capacitor structures have been studied. Under constant‐voltage stressing, the current density through the 1500‐A‐thick lead‐zirconate‐titanate (PZT) film exhibits a power‐law dependence on time, with the exponent (∼0.33) independent of temperature and voltage. Electrode material dependence of current density indicates that the conventional model of trap‐limited single‐carrier injection over nonblocking contacts is inadequate to explain the time‐zero current. A change in top electrode material from Pt to In leads to the observation of work‐function‐driven Schottky contacts between the metal and ferroelectric. The current‐voltage characteristics fit a two‐carrier injection metal‐semiconductor‐metal model incorporating blocking contacts, with distinct low‐ and high‐current regimes (PZT is assumed to be p‐type and trap‐free in this model). Temperature‐dependent I‐V measurements indicate a Pt‐...

A model for electrical conduction in metal‐ferroelectric‐metal thin‐film capacitors

A method for forming CMOS transistors and ferroelectric capacitors on a single substrate (10) with improved yield begins by forming CMOS transistors (37a, 37b, 40, 42). A hydrogen anneal using 4-5% hydrogen and a remainder nitrogen is performed to reduce dangling atomic bonds at the gate dielectric/substrate interface of the transistors (37a, 37b, 40, 42). A silicon nitride layer (48) is then deposited over the transistors and on the backside of the wafer substrate (10) in order to substantially encapsulate the effects of the hydrogen anneal to the CMOS transistors (37a, 37b, 40, 42). Ferroelectric capacitor layers (54, 58, 60, 62, 64) are formed overlying the nitride layer (48) where the ferroelectric capacitor layers (54, 58, 60, 62, 64) are oxygen annealed in pure O 2 . The nitride layer (48) prevents the transistor hydrogen anneal from damaging the ferroelectric material by containing the hydrogen.

Method for making a ferroelectric device

Interfaces and hence electrodes determine the performance of (Ba,Sr)TiO3 (BST) capacitors for ultralarge scale integration dynamic random access memories. Electrode materials forming a rectifying contact on BST drastically reduce the dielectric constant and hence the capacitance and charge storage density of the capacitor, when the dielectric thickness is reduced. This can limit the role of Pt as an electrode material for gigabit dynamic random access memories (DRAM). The conducting oxide, La0.5Sr0.5CoO3 (LSCO) with its perovskite structure, has structural and chemical compatibility with BST. Our results in LSCO/BST/LSCO capacitor show that the mechanism of conduction is not interface limited but predominantly bulk limited. A 75 nm BST film with LSCO electrodes shows a leakage current density of 1×10−7 A/cm2 at 1 V, 85 °C. The dielectric constant at 1 V, 105 Hz is 350, making LSCO a potential contact electrode for DRAM memories.

(Ba,Sr)TiO3 thin films with conducting perovskite electrodes for dynamic random access memory applications

We report on the properties and characterization of SrBi 2 Ta 2 O 9 (SBT, or Y − 1) thin film capacitors for ferroelectric random access memory (FERAM) applications. The films were prepared by spin-coating from carboxylate precursors. The remanent polarization ( P r ) was 5−6 μ C/cm 2 and the coercive field was ∼55 kV/cm. Excellent fatigue endurance was observed up to 10 11 cycles. Auger analysis indicates bismuth diffusion through the Pt electrode after capacitor anneal which might require excess Bi in the precursor solution for stoichiometry control. No detectable amount of α emission was found from SBT films, which reduces the possibility of soft error when used in the memory devices.

Robert E. Jones

Papers

Ferroelectric non-volatile memories for low-voltage, low-power applications

A model for electrical conduction in metal‐ferroelectric‐metal thin‐film capacitors

Method for making a ferroelectric device

(Ba,Sr)TiO3 thin films with conducting perovskite electrodes for dynamic random access memory applications

Characteristics of spin-on ferroelectric SrBi2Ta2O9 thin film capacitors for ferroelectric random access memory applications