Development of large-area 200-volt planar voltage-variable capacitance diodes

A research and development program resulted in fabrication of high-capacitance voltage-variable capacitance diodes for electronic tuning. Devices were fabricated by epitaxial and planar technology, with the diode prepared by diffusion into n-type silicon to approximate an abrupt junction. Objective specifications required devices with capacitance of 250 pF and 1000 pF (-8V), breakdown voltage V, capacitance change ratio of > 5.6 (-4 to -200 V), and quality factor (10 MHz). The principal problem was the limitation of planar diodes, which results in part from the tendency of thermally oxidized n-type Si to form an accumulation layer in the Si at the Si-SiO2interface. The planar process was refined to achieve large-area 200-V planar diodes, while maintaining the other essential diode characteristics, by the introduction of modifications to lower the electrical field of the p-n junction at the surface. Both structural modifications and processing changes were found to result in an increase in the level of of planar diodes.