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Amorphous Rare Earth Transition Metal Ternary Alloys for Thin Film Resistor Networks

IP.com Disclosure Number: IPCOM000049456D
Original Publication Date: 1982-Jun-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Ruf, RR: AUTHOR

Abstract

Nonmagnetic, amorphous, rare earth transition metal alloys, such as Gd-Co-Mo, can be sputtered or evaporated onto room temperature substrates which are stable up to 350 degrees C. They have resistivities that are typically 200 to 250 micro ohm-cm. This is roughly twice as high as other contending metallic systems, such as Ni(80) Cr(20) (110 micro ohm-cm). The resistivities can be increased by deposition in a low partial pressure of oxygen. The rare earth constituent preferentially oxidizes to form a stable oxide, such as Gd(2)O(3). Bias sputtering in an inert gas with the usual residual amount of oxygen is especially useful since with the bias voltage applied, it preferentially resputters the oxide, allowing precise control of the oxygen concentration.

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Amorphous Rare Earth Transition Metal Ternary Alloys for Thin Film Resistor Networks

Nonmagnetic, amorphous, rare earth transition metal alloys, such as Gd-Co-Mo, can be sputtered or evaporated onto room temperature substrates which are stable up to 350 degrees C. They have resistivities that are typically 200 to 250 micro ohm-cm. This is roughly twice as high as other contending metallic systems, such as Ni(80) Cr(20) (110 micro ohm-cm). The resistivities can be increased by deposition in a low partial pressure of oxygen. The rare earth constituent preferentially oxidizes to form a stable oxide, such as Gd(2)O(3). Bias sputtering in an inert gas with the usual residual amount of oxygen is especially useful since with the bias voltage applied, it preferentially resputters the oxide, allowing precise control of the oxygen concentration. Typical oxygen concentrations are from almost zero to ten atomic percent, resulting in resistivities that can be varied from 200 to about 10,000 micro ohm-cm. These high resistivities result in significant reduction of the resistor length. In addition, it is possible to laser beam trim the resistors after fabrication by crystallizing selected areas, resulting in a 50 percent reduction of the resistance in those areas.

Cermet compositions, such as Au-SiO(2) and Au-Ta(2)O(3), have comparable resistivities, but are difficult to reproduce and require a post deposition annealing treatment to stabilize the composition. Temperature Coefficient of Resistivity (TCR)

It is well known that amorphous metal alloys have lower TCRs than their crystalline counterparts. I have found that rare earth transition metal films with high resistances due to oxygen incorporation behave similarly. A measured amorphous film of Gd-Co-Mo that was sputtered in a background pressure of oxygen had a resistivity of 5000 Mu Omega cm and a TCR of only 650 PPM at room temperature. A TCR of 1000 PPM is considered good for polysilicon resistors and 2000 PPM for diffused silicon resistors. Apparently, an insulating Gd(2) O(3) phase forms which decreases the effective...