Negative resistance devices

Case (a). The negative resistance device has a I—V characteristic which is retraceable except for some hysteresis which is observed when the current is changed too rapidly for maintaining thermal equilibrium. An example of this is the well known thermistor. By using a small load resistor R this negative resistance device can be made to switch from a point (A) where the... 

Fig. 6.1. Classification of switching and memory characteristics, (a) Negative resistance device, (b) Negative resistance device with memory, (c) Switching device, (d) Switching device with memory, (e) Voltage controlled negative resistance device with memory.

Case (b). The negative resistance device with memory has two stable states. The first state resembles that of case (a). The second is conductive. It is established at higher currents and remains without decay. The first state can be reset by increasing the current above a certain value and switching it off rapidly. These effects were observed in oxides and chalcogenides by Dewald et al (1962), Pearson et al (1962, 1964), and Eaton (1964). In some cases the polarity of the reset current must be opposite to that of the set-on current. Such polar effects appear to be strong whenever electromigration dominates as will be discussed later. 

Typical positive temperature coefficient (PTC) device behavior for a doped polycrystaHine BaTiO thermistor is presented in Figure 4. At temperatures below - 100° C and above - 200° C the material shows the expected negative resistivity vs temperature associated with semiconductors as expressed by ... 

Molecular Rectifiers and Negative Differential Resistance Devices. 234... 

The first resist used to fabricate solid-state devices was a negative resist based on cyclized poly(cis-1,4-isoprene) which is crosslinked using a photoactive bis-... 

Radiation-sensitive polymers are used to define pattern images for the fabrication of microelectronic devices and circuits. These polymers, called resists, respond to radiation by either chain scission (positive resists) or by crosslinking (negative resists). In positive resists, the exposed areas dissolve selectively by chemical developers in negative resists, the exposed areas are insoluble and remain after development. 

A mixed ion conductor, BaSnO, has also been tested as a contact layer on a Schottky sensor [90]. The BaSnOj/SiC sensor showed a response to oxygen and this was most pronounced at 400°C. The sensor was tested from 200°C to 700°C. Operated at 700°C, the sensor showed a negative resistance peak at a bias of 2V (Figure 2.8). This peak was accounted for by the tunneling or Esaki effect [91]. Up to an operation temperature of 400°C, thermionic emission was proposed to explain its behavior. At higher temperatures, a resistance connected in series with a Schottky diode can model the device [5, 73]. At temperatures of 500-600°C, the BaSn03 shows a mixed behavior of electronic and ion conduction, and the Nernst potential [92] can be added to the model. The complete proposed model is given in (2.9). 

For non-ohmic resistors, R is a function of current and the definition R = dV/dl is far more useful. This is sometimes called the dynamic resistance. Solid state devices such as thermistors are non-ohmic, and non-linear. A thermistor s resistance decreases as it warms up, so its dynamic resistance is negative. Tunnel diodes and some electrochemical processes have a complicated /-Vcurve with a negative resistance region of operation. 

Figure 4.15. Top Cross section of a MISS diode. The device can be regarded as a reverse-biased metal-insulator-semiconductor diode in series with a for-ward-biased n-p Junction. It then exhibits two stable states separated by an unstable negative resistance region. Bottom Current-voltage characteristics for a GaAs-(j -TA MISS device. The LB film thickness is approximately 9 nm...

A silicon wafer was cleaned with ethanol and coated with a thin layer (about 0.5 pm) of 2.8e (3% solution in THF) by the application of a spin-coater. Irradiation through a mask (or any other device which provides irradiated and unirradiated zones) with UV light. X-rays or electron beams generated a pattern which was developed by a short immersion into THF. The unchanged polymer was dissolved and the irradiated parts with the crosslinked polymer remained. (Principally, this imaging technique with a negative resist... 

The hexaacetate of 6 has been tested as a high resolution negative resist for electron beam lithography, showing sufficient resolution to be useful for nanoscale device processing. Quantum confined cadmium sulfide clusters are stabilized by the Mannich base calixarenes 195 (R = Me, Bu, cyclohexyl). ... 

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