Voltage-controlled Negative Resistance Research Articles

Invited paper A critical review of the observed electrical properties of MIM devices showing VCNR

Some insulating films of thickness normally between 10 nm and 600 nm in both sandwich and planar configurations (MIM devices) undergo a forming process in which the formed devices acquire a permanently, irreversibly enhanced conductivity, The I(V) characteristics with a region of voltage-controlled negative resistance (VCNR) are influenced by the fabrication methods, electrode metals and ambient conditions such as temperature and pressure. The emission of electrons through the top electrode becomes most apparent at the onset of the VCNR region. Switching and memory phenomena are also observed. In this paper we present a critical analysis of various electrical properties of MIM devices, with supporting experimental evidence.

Further studies on the electroforming of thin films of evaporated polypropylene

Further work on the electroforming of metal-polypropylene-metal (MIM)structures under different pressure and temperature is reported. The electroformed samples show voltage controlled negative resistance (VCNR) and emit electrons into a vacuum. The results are consistent with the theory based on the filamentary model of conduction.

Some electrical properties of thin film sandwich assemblies of SiO/V2O5

Thin films of the complex dielectric material SiO/V2O5 were prepared by a co-evaporation technique and used as the insulator material in MIM structures in which the metal M was copper. Most of the samples could be electroformed at between 4 and 9 V applied. They then exhibited a voltage-controlled negative resistance associated with an emission current into vacuum whose density was of the order of 10−5 A cm−2. Voltage-memory, thermal voltage-memory and ambient pressure-memory effects were also observed. A polyfilamentary model was used to interpret these properties.

Some electrical properties of amorphous thin films of mixed SiO and TiO

Electrical conduction in Cu-SiO/TiO-Cu thin film structures has been investigated. Prior to electroforming, the d.c. conduction showed a behaviour of the form log lc∞(Vb)1/2 where lc is the circulating current and Vb is the applied voltage. At low applied voltages the a.c. conductivity obeyed the relation σAC∞fn (n=0.82 at 209 K). After electroforming, the samples showed voltage controlled negative resistance (VCNR), electron emission and voltage memory effects which can be explained in terms of a filamentary model.

The effects of filamentary conduction through uniform and flawed filaments in insulators and semiconductors

Electrical conduction through relatively low resistance filaments has been proposed as the mechanism whereby current-controlled negative resistance (CCNR), voltage-controlled negative resistance (VCNR), switching and memory effects take place, particularly in amorphous insulators and semiconductors. Two types of filament are considered: uniform filaments (in which the applied voltage is assumed to drop uniformly along the filament's length) and non-uniform filaments (in which the applied voltage drop occurs primarily at a higher resistance flaw within the filament). By regarding heat dissipation as taking place either uniformly or preferentially at flaws, depending on the filament type, expressions are derived for the temperature within the non-conducting insulator or semiconductor regions, filament or flaw temperature, and voltage at which a filament will cease to conduct. It is shown that for uniform filamentary conduction in thin films the conduction in individual filaments is influenced by the number and proximity of neighbouring filaments, while flawed filaments are essentially isolated from their neighbours. An illustration in the application of the model is given (in the case of uniform filaments) for an assembly of conducting filaments, and various filamentary parameters are calculated. Experimental evidence for a range of different systems is reviewed, and shown to be consistent with the model.

A new high-power voltage-controlled differential negative resistance device—The lambda bipolar power transistor

A new high power voltage-controlled differential negative resistance device using the LAMBDA bipolar transistor structure, called the LAMBDA bipolar power transistor, is proposed and studied. The basic structure of this new device consists of the simultaneous integration of an interdigitated bipolar junction transistor and a merged metal-oxide-semiconductor field effect transistor. Two basic interconnection configurations of the integrated devices are also discussed. Several interesting applications based on the fabricated devices are also demonstrated. It is shown that the proposed device can be used as power signal generator and amplitude modulator using very simple circuits.

Voltage-temperature memory and pressure-voltage memory effects in coevaporated films of SiOTiO

Sandwich structures of Cu/(SiOTiO)/Cu where the thickness of the coevaporated insulator is in the range 2000–13 000 Å were investigated. Electroformed devices show voltage-controlled negative resistance, electron emission, pressure-voltage memory and thermal-voltage memory effects. The effects of an increase in pressure or a decrease in temperature on the electrical behaviour of a formed sample are similar in form. The results can be interpreted in terms of the filamentary model of electrical conduction as proposed by Dearnaley, Morgan and Stoneham.

On the Structural and Electronic Characteristics of Titanium Sulphide (Tis1.7) Crystals

AbstractTiS1.7 crystals have been grown by vapour transport technique employing a two‐zone furnace with the temperatures of reaction and growth zone maintained at 1073 K and 973 K, respectively. We have measured the variation of electrical conductivity (s̀) with temperature (T) of TiS1.7 single crystals. It has been found that the conductivity increases at temperatures T > 433 K, which provides convincing evidence that the TiS1.7 crystal is a semiconductor. Another electronic characteristic of TiS1.7 crystals observed in the present investigation is the occurrence of voltage controlled negative resistance (VCNR) at a field of 32.1 V cm‐1 to 35.7 V cm‐1. All the polytypes of TiS1.7 were found to exhibit VCNR nearly at the same field which indicates that the VCNR is polytype independent property. The occurrence of VCNR has been explained on the intervally transfer of electrons in the conduction band.

The new general realization theory of FET-like integrated voltage-controlled negative differential resistance devices

A new general realization theory of FET-like voltage-controlled negative differential resistance device is presented. A feedbacktransfer model (FTM) of the FET, which contains four different kinds of feedback connections and their own mathematical conditions, is set up. Based on this model, a general simple realization technique is explored. Using this technique many negative differential resistance FET-like integrated devices either new or published are generated, and their integrated circuit configurations and basic properties are studied and discussed. Application example for a specific device is demonstrated, which substantiates the exactness of the proposed theory.

Evidence for the contribution of an adsorbate to the voltage-controlled negative resistance of gold island film diodes

The electroforming of gold island films with voltage-controlled negative differential resistance (VCNR) characteristics was found to be possible only under certain specific surrounding condition, e.g. in a high vacuum system evacuated with an oil diffusion pump, but not in an ultrahigh vacuum. In the latter case exponential high resistivity curves were obtained; VCNR forming is possible, however, after transference of the diodes to a high vacuum.

Electrical properties of GeO2films

Measurements have been made on thin films using Ge${\mathrm{O}}_{2}$ as the dielectric material and for thickness ranges from 130 to 2000 \AA{}. These thin layers of Ge${\mathrm{O}}_{2}$ show a number of interesting electrical properties which include electroforming, voltage-controlled differential negative resistance, electroluminescence, electron-emission, and switching-memory effects. A theory is developed in terms of the growth and thermal rupture of many conducting filaments through the insulating layer to explain the observed voltage-controlled differential negative resistance, electron-emission, electroluminescence, and memory phenomena.

Electrical behavior of polyvinylchloride thin films

While investigating the metal–polyvinylchloride (<1500 Å)–metal sandwich structure using Al, Ag, Cu, and In electrodes, two kinds of switching properties were found. The symmetric sandwiches with aluminum electrodes exhibited voltage-controlled negative resistance (VCNR) with memory, while asymmetric structures displayed current-controlled negative resistance (CCNR) with memory. It was not possible to observe both kinds of switching phenomena in a single sample. The VCNR mechanism may be explained on the basis of high-field domains (or an accumulation layer) and the CCNR phenomenon may be explained on the basis of a filamentary model.

Electrical characteristics of r.f.-sputtered Al 2O 3 MIM structures

The voltage-controlled negative resistance (VCNR) and switching characteristics of r.f.-sputtered Al 2O 3 MIM structures were investigated as functions of pressure and temperature. Above a certain critical pressure in the region of 0.1 Torr, VCNR and transient effects fail to occur and the junctions remain in a low conductivity state. We also observe that for junctions held in ambient temperatures of below 200 K no VCNR or switching effects occur and the junction remains in a low conductivity state. We conclude that neither filamentary nor tunneling models provide completely satisfactory descriptions of the transport mechanisms involved for the structures examined.

A new photo-sensitive voltage-controlled differential negative resistance device—The lambda bipolar photo-transistor

A new photo-sensitive voltage-controlled differential negative resistance device called the LAMBDA bipolar photo-transistor is presented. The basic structure of the Lambda bipolar photo-transistor consists of the simultaneous integration of a bipolar junction transistor and a merged metal-oxide-semiconductor field effect transistor. The IV characteristic of this new device will exhibit a voltage-controlled differential negative resistance when the device is exposed to light. The operational principle of this new device will be described and the characteristics of the fabricated device are discussed.

Generalized theory and realization of a voltage-controlled negative resistance MOS device (lambda MOSFET)

A generalized theoretical approach used to predict circuits which exhibit the three-terminal negative resistance MOS characteristic is presented. The main structure of the positive feedback circuit is accomplished by connecting the drain and gate terminals of an n-channel enhancement mode MOSFET with the input and output terminals of an inverter circuit. The characteristic parameters such as the peak current, the peak voltage, the negative resistance, and the valley voltage are derived in a generalized form. Based on the theoretical predictions, several high density integrated circuits that give rise to a voltage-controlled negative resistance characteristic were fabricated and are described.

A new integrated voltage-controlled negative resistance device-Lambda MOSFET

A new Λ-type voltage-controlled negative resistance device called the “Lambda MOSFET” is presented, which consists of three integrated n( p)-channel enhancement mode metal-oxide-silicon field effect transistors. The main integrated circuit construction of the Lambda MOSFET is to connect an inverter of the n( p)-channel enhancement mode MOSFET with load operated at the saturation region (NELS) and a n( p)-MOS driver, which can be easily fabricated by existing planar MOSFET technologies. The operational principles and the characteristics of the proposed new device are discussed.

A study of gold migration in Au-Y 2O 3-Y junctions by secondary ion mass spectrometry

Secondary ion mass spectrometry has been used to detect the migration of gold from the electrode into the oxide layer of Au-Y 2O 3-Y junctions during the electroforming process. The depth profiles obtained showed an increase of gold migration after the development of conductivity and again after the appearance of a voltage-controlled negative resistance when a forming voltage was applied. The results are discussed in terms of localized conduction at defects which are observed on the junction surface.

An improved GAMBIT device structure

An improved device structure is presented for the gate modulated bipolar transistor (GAMBIT). By forming vertical walled collector regions, the GAMBIT voltage-controlled negative-resistance characteristic has been made to occur at low collector voltages without the presence of the threshold voltage observed for the planar diffused devices. The negative resistance of these devices varies exponentially with the reciprocal of the gate bias and increases with collector depth as expected from analysis.

Forming process, i-v characteristics and switching in gold island films

Some experimental results are presented concerning the electrical properties and electron microscope observations of discontinuous gold island films on an insulating substrate. Electron microscope observations during the electrical operation identified the so-called forming process as coagulation of a thin continuous gold film. Some rules for the development of a voltage-controlled negative resistance portion of the I-V characteristic are formulated. Switching occurs when point contacts are used. The results presented are in agreement with a model on related subjects proposed by Dearnaley et al., who postulated a filamentary conduction state. Some modifications concerning rupture of the filaments are necessary however.

A new switching effect in M-I-M thin-film structures at atmospheric pressure

Our M-I-M. thin-film structures based on the SiO/BaO complex can undergo either an electroforming process and show voltage-controlled negative resistance (VCNR) or a now switching process. Switching characteristics have been measured and interpreted using a monofilamentary model in contrast with the polyfilamentary model of Deaenaley et al. Parameters which control the thermal dissipation from the sample have boon found effective in determining the switching characteristics.