Amorphous Metals
Amorphous metals uniquely provide a critical benefit to thin film electronics. Both amorphous metal oxide semiconductor and quantum tunneling thin film electronic devices function in response to an electric field - the greater the field strength, the higher the electrical current produced in the device. However, the uniformity of the distribution of energy across the field has a dramatic impact on both mobility and stability of that current. The energy distribution across the field is the result of the uniformity of the insulator’s dielectric constant and the uniformity of the spacing between the two electrodes forming the capacitor where the field is generated. Uneven energy distribution causes concentrations of current density in quantum tunneling devices, and increases charge scattering in amorphous metal oxide semiconductor devices. The former causes device failure; the latter reduces device mobility and stability.
Amorphous metals’ smooth surface relative to crystalline metals maximizes energy distribution across the capacitance. As the chart at left demonstrates, amorphous gate metals uniquely enable thinner gate insulators, thus increasing gate electric field energy and increasing field effect mobility.
The challenge of using high electric field energy lies with the potential for nonuniformities in the field - nonuniformities that translate to the surface potential induced across the semiconductor by the field, or in the tunneling field itself. These field nonuniformities scatter charges in the conduction channel, reducing the speed of charges traversing the channel through diffractions that increase charge mean free path. These nonuniformities cause charge scattering resulting from the roughness of a remote surface - the gate metal surface.
An amorphous metal (also known as metallic glass, glassy metal, or shiny metal) is a solid metallic material, usually an alloy, with disordered atomic-scale structure. Most metals are crystalline in their solid state, which means they have a highly ordered arrangement of atoms. Amorphous metals are non-crystalline, and have a glass-like structure. But unlike common glasses, such as window glass, which are typically electrical insulators, amorphous metals have good electrical conductivity and can show metallic luster.
Amorphous metal is usually an alloy rather than a pure metal. The alloys contain atoms of significantly different sizes; their viscosity prevents the atoms moving enough to form an ordered lattice. Amorphous metals, while technically glasses, are also much tougher and less brittle than oxide glasses and ceramics.
Minimizing remote surface charge scattering isn’t the only way an amorphous gate metal improves amorphous metal oxide TFT mobility. The results of experiments performed by Amorphyx (shown at right) clearly indicate the surface roughness of the gate insulator interface with the semiconductor is defined by the surface roughness of the gate metal. An amorphous gate metal not only minimizes remote surface charge scattering, it also minimizes charge scattering due to insulator-semiconductor surface roughness.
