John Martin Shannon

A majority‐carrier camel diode

A majority‐carrier diode concept is described in which current flow is controlled by a potential hump in the bulk of a semiconductor. Devices of this type, called camel diodes, having ideality factors <2 have been realized using low‐energy ion implantation.

Current induced drift mechanism in amorphous SiNx:H thin film diodes

It is shown that the drift in the current–voltage characteristics of silicon‐rich amorphous silicon nitride metal–semiconductor–metal diodes can be explained by a mechanism whereby electron trapping centers are created via hole–electron recombination. A first order model which includes excitation of holes by hot electrons moving into the anode and recombination of electrons with holes trapped in the valence band tail is in good quantitative agreement with the measured dependencies between drift, device thickness, current density, time, and charge passed through the device.

Tunneling effective mass in hydrogenated amorphous silicon

The tunneling effective mass of electrons in undoped a‐Si:H has been determined from measurements on Schottky diodes operating with high reverse fields. Under these conditions, the change of current with electric field is a sensitive function of effective mass. The tunneling effective mass was measured to be 0.09±0.02 me for a range of different samples giving a tunneling constant of ≊40 A.

Light degradation and voltage drift in polymer light-emitting diodes

It is shown that the voltage drift and light degradation in polymer light-emitting diodes are related and can be explained by the formation of traps and the modification of the space charge in the bulk of the polymer. The energy released by nonradiative carrier recombination is believed to be the driving force for the generation of traps in poly(p-phenylene vinylene) conjugated polymers. A first-approximation model is derived for the voltage drift and the light decrease during operation, which is in good agreement with experimental observations for time and current density dependencies.

Passive and active matrix addressed polymer light-emitting diode displays

Polymer LEDs provide a new alternative to LCDs for many display applications, and are particularly attractive because of their high brightness, near-perfect viewing angle, and very fast response time. In this paper, the basic technology used to form the LED structures, and the performance of these devices is presented. Then, the fabrication and driving of passive addressed matrix displays formed using this technology is discussed. Finally, the necessity for active matrix addressing for larger size and higher resolution displays is demonstrated, and it is shown that this is best achieved using low temperature poly-Si technology. The state-of-the-art poly-Si technology used for active matrix addressed LED displays is described, with particular reference to transistor variation, and the resulting non-uniformities in images on displays. A variety of different addressing techniques, and pixel circuits can be used to drive the LEDs in the active matrix, and the performances of these schemes are compared. These include the basic current source circuit; the modified current source circuit; transistor current mirror circuits; and circuits with optical feedback and correction for uniformity variation. Consideration is given both to analogue and to digital drive methods.

Electronic Properties of a-SiN x :H Thin Film Diodes

With a semiconductor memory cell (particularly but not exclusively in a thin-film device) having a non-volatile memory transistor (Tm) as a driver transistor, an adequate difference in output signal (I) can be derived from the cell for the different states of the memory transistor (in spite of poor transistor characteristics,) thereby permitting the assembly of a large number of such memory cells in an array (100). Each memory cell includes a load (TI) driven by the non-volatile memory transistor (Tm). In the different memory states of the memory transistor (Tm) a difference in signal occurs at a node (30) between the memory transistor (Tm) and the load (TI). Each cell also includes a switch (To) which is coupled to the node (30) and switched from one output state to another by the signal at the node (30). The output state of the switch (To) provides the output signal (I) from the cell. Such an arrangement permits the memory transistor (Tm) and the output switch (To) to be optimized for their respective memory function and output function. The memory transistor may be of the dielectric-storage type (MNOST) or of the floating-gate type. In a thin-film circuit memory, the output switch may be a thin-film transistor (To) or a thin-film diode.

Improved optical feedback for OLED differential ageing correction

— To compete with LCDs and to meet standard display product specifications, OLED displays must have a high degree of tolerance to differential ageing or “burn-in.” A new optical feedback pixel circuit is presented that enables accurate differential ageing correction, can have low power consumption, and enables a high degree of non-uniformity correction. The circuit can be implemented in LTPS, and a-Si:H TFT technologies and circuits for both cases are shown. The a-Si:H approach is low cost and enables correction of both TFT threshold voltage drift and OLED degradation at the same time. The circuit analysis, operation, and technology will be described and results presented.

35.2: Improved Optical Feedback for AMOLED Display Differential Ageing Compensation

A new optical feedback pixel circuit is presented that enables a high degree of differential ageing correction, has low power consumption compared to standard AMOLED pixel circuits and enables a high degree of non-uniformity correction. The circuit operation and the technology used to construct it will be described and results presented.

Thermionic emission in bulk unipolar camel diodes

An analysis of the current‐voltage characteristics of bulk unipolar camel diodes in GaAs with a high doping concentration in the barrier region has concluded that current transport is close to the thermionic limit.

I‐V impurity profiling with a Schottky barrier

A method is described for determining the impurity profile beneath silicon Schottky diodes at room temperature when current transport is dominated by thermionic‐field emission of electrons. The technique may be used when depleting between 1012 and 1013 charges cm−2.