Kunihiko Wada

A new programmable cell utilizing insulator breakdown

A new programmable cell called the Breakdown-of-Insulator-for-Conduction cell (BIC cell) has been proposed and developed. A BIC cell utilizes the electrical breakdown of an insulator for programming. A highly refined thin insulator, with a delta-function type of breakdown voltage distribution, is employed in the BIC cell. This cell can be programmed within 1 µsec, making it possible to realize the shortest programming time for PROM cells reported so far Programmed cell resistance is around 1×102ohms. Since a BIC cell has a stacked-cell structure, a PROM cell can be formed simply by merging a BIC cell with a MOSFET. Then, a PROM cell array can be formed from these cells. A programming method for a PROM cell array is discussed below.

Elastic calculation of the thermal strains and stresses of the multilayered plate

An elastic calculation has been carried out on the thermal deformation strains, and stresses of a multilayered plate (MLP) which is composed of a circular substrate and thin films on it. The MLP is assumed to be constructed with no initial stresses at a temperature T0, and to be given a temperature change ΔT. In the calculation, the variation method has been utilized in such a manner as to minimize the total Helmholtz‐free energy of the MLP by varying its shape of deformation. Without using the assumption of the plane stress state, a closed form solution has been obtained which determines the radius of curvature of the warpage, strains eij (i, j=x,y,z) and stresses τij in each layer by ΔT, αm the thermal expansion coefficient, Em the Young’s modulus, σm the Poisson’s ratio, and tm the thickness of each layer. The solution obtained has reproduced the plane stress state as an approximate description of the deformation. A solution in the case of the large radius MLP, where the effect of the shear strains has...

A new cell for high capacity mask ROM by the double LOCOS technique

A new cell for use in an extremely high-capacity mask ROM has been developed by using the Double LOCOS (DL) technique. This cell, called a SADL cell (Self-Aligned cell by DL technique), realizes4F^{2}area (F: minimum feature size) using a fully self-aligned fabrication process. The area of the new cells can be reduced to 1/2 of that of ordinary ROM cells, even when fabricated with conventional silicon IC technology. A 4K-bit SADL cell array was fabricated using 2-µm (diffusion line width) and 3-µm (field line width) rules, realizing a cell size of 25 µm2, the smallest reported so far. In the SADL cell, conductance is large because it is determined by the forward-biased diode characteristic. A high-speed readout method may be adopted for further speed improvement.

Far-infrared absorption by oxygen in silicon

Far‐infrared absorption measurements in the 14–50 cm−1 range have been performed for oxygen containing silicon crystals in a temperature range of 4.2–35 K. In addition to the previously reported absorption peaks at 29.3, 37.8, 43.3, and 49.0 cm−1 [D. R. Bosomworth, W. Hayes, A. R. L. Spray, and G. D. Watkins, Proc. R. Soc. London A 317, 133 (1970)], a fine structure with peaks at 25.3, 28.3, 30.2, and 33.3 cm−1 has been found, which is considered to be a sideband caused by a coupling between the off‐center excitation of the interstitial oxygen and other anharmonic localized excitation of an energy of about 1 cm−1 hc.