J. De Baets

Polycrystalline CdSe films for thin film transistors

Abstract In this paper X-ray, ESCA, TEM and electrical measurements on evaporated CdSe films, used in thin film transistors (TFT), are reported. Special attention has been paid to semiconductor films obtained from recrystallized mixtures of CdSe and 1–2% In 2 Se 3 . Such films might be represented as (3CdSe) x (In 2 Se 3 ) 1- x . Doping the CdSe evaporation source with In yields 20 μm self-aligned TFTs with excellent characteristics: electron mobility in the evaporated thin films increases from 20–50 cm 2 /V · s for undoped films to more than 100 cm 2 /V · s for doped films. DC stability behaviour is also improved: the TFT current drop after 180 s is reduced from 30% to less than 5%.

Stabilizer Concentration and Local Environment: Their Effects on Electroless Nickel Plating of PCB Micropads

With the advent of flip chip assembly, pads to be plated on printed circuit boards (PCBs) have shrunk dramatically to around . As a result, most commercial electroless nickel baths will fail to deposit nickel on such small micropads. In this paper, using a specially designed PCB layout, the effects of concentration and local environment are studied. A competition mechanism between two opposite actions, the adsorption from bulk solution by diffusion and the burying by nickel deposition, is used to explain the effect of as a catalytic inhibitor. On a constantly growing surface, the dynamic density of adsorbed is the net result of these two opposite actions. Using this competition mechanism, the skipping problem of micropads is attributed to the combined result of nonlinear diffusion and high concentration of in the bulk solution. This competition mechanism also gives a new explanation for the effect of potential pinning. In the case of potential pinning, galvanic effect by electrons flowing from one area to another only exists during the initial period of nickel deposition. Once it is started, nickel deposition on any area is maintained by the electroless process, and hence, is actually self‐supporting, By reducing the bulk concentration of to a lower range in a commercial bath, we have realized consistent nickel plating on micropads as fine as 50 μm in diameter.

2-MHz clocked LCD drivers on glass

A poly-CdSe thin-film transistor (TFT) liquid crystal display (LCD) driver circuit which is integrated on the display itself, reducing the interconnections to the display, is described. The circuit can be used to drive the rows as well as the columns of active and passive matrix LCDs. Drivers made in a 25- mu m technology operate at frequencies up to 2 MHz. Simulations indicate a maximum operating frequency of 8 MHz for a 12.5- mu m technology. By using a time-multiplexing addressing scheme, gray scales can be obtained. In order to address high-resolution displays with gray scales, parallel operating drivers can be used, requiring only one extra connection per parallel driver. >

On the field effect in polycrystalline CdSe thin-film transistors

Based on the grain barrier model of Levinson an expression of the off‐current Ioff of a thin‐film transistor is derived.The dependence of Ioff on the donor concentration ND and the semiconductor thickness ds is discussed and compared to experimental data. It is shown that NDds has to be smaller than the grain‐boundary trap concentration in order to obtain enhancement thin‐film transistors completely turned off at VG=0.

High-voltage polycrystalline CdSe thin-film transistors

The properties of self-aligned high-voltage CdSe thin-film transistors (TFTs) are described. By analyzing the different failure mechanisms, it is found that In-doped CdSe makes device operation up to 200 V feasible. Furthermore, the high-voltage CdSe TFT shows excellent low off currents and high transconductance. >

Evaluation of a 64 x 64 CdSe TFT addressed ACTFEL display demonstrator

An operating ACTFEL (AC thin-film electroluminescent display), addressed with TFTs, has been demonstrated. To achieve this, the authors used self-healing electrodes, limited the power supplied to the display, and used a stepped annealing cycle for the TFTs. The display could be driven with 10-V external drivers at a frame rate of 50 Hz and an EL driving frequency of 100 Hz.<<ETX>>

CdSe-based thin-film integrated optical sensors

Abstract A fabrication method for photoconductive CdSe films, together with a photolithographic process is presented. Two types of films were realized. The first type has a low resistivity (102 Ω cm), a moderate sensitivity and is semi-transparent. The second type of film has a high resistivity (108 Ω cm) and is very sensitive. It is shown that the films meet the requirements of two applications: a luminance sensor and a linear image sensor.

A new technology for fast switching circuits on glass

A low-temperature self-aligned photolithographic process is described to fabricate fast switching digital poly-CdSe thin-film transistors (TFTs) on glass, The use of sintered CdSe-In2Se3mixtures as an evaporation source for the semiconductor resulted in TFTs with attractive static and dynamic characteristics. The measured inverter delay for a 20-µm technology was 75 ns.

Thin Film Cadmium Selenide Technology in Large Area Active Matrix High Resolution Displays

This paper considers the acceptability of an active matrix technology based on thin film polycrystalline CdSe for the industrial manufacture of large area high pixel density active matrix flat panel displays.

The influence of low copper doping concentrations on the recrystallization process in and the electrical properties of germanium in Ge:Cu thin film transistors

Abstract The electrical properties of copper-doped germanium (Ge:Cu) thin films were investigated as a function of the copper concentration and the annealing temperature. Measurements of the sheet resistance indicated that copper concentrations as low as 0.1 at.% still have a significant influence on the recrystallization process in germanium. This was also demonstrated by experimental data on the effective field effect hole mobility. These results are explained on the basis of a “grain path model”. From measurements of the threshold voltage of Ge:Cu thin film transistors, we found that oxygen, incorporated in the grain boundaries of the recrystallized Ge:Cu thin films, has a pronounced impact on the field effect in these films. An accurate control of the oxygen content in the Ge:Cu films even allows us to optimize the electrical parameters of our Ge:Cu thin film transistors.