Advanced tunnel dielectrics for floating-gate nonvolatile memory applications

As the demands for higher densities and lower supply voltages increase in floating gate nonvolatile memory devices, the necessity to reduce the internal programming voltage is a critical issue. Reducing the internal programming voltage relieves constraints placed on the charge pumping circuitry and reduces the area and the complexity needed for the peripheral circuitry related to high voltage operation which consumes a significant portion of the chip. Reducing the programming voltage can be achieved by scaling the tunnel oxide thickness or by using alternative dielectrics with reduced effective tunneling barriers. Both approaches are investigated.; Scaling the tunnel dielectric brings about reliability issues such as data retention and endurance cycling. Charge retention has been investigated as the programmed threshold voltage was reduced which reduces the electric field. At thickness down to 65A, long term charge retention was observed provided the electric field was held below 2MV/cm. Between 47A and 65A the electric field must be further reduced to maintain long term data retention. The program/erase cycling endurance was found to improve as the tunnel dielectric thickness was reduced.; The second approach utilizes the current conduction properties of RTCVD oxides post annealed in N{dollar}sb2{dollar}O to improve the Fowler-Nordheim programming performance. The use of the RTCVD oxide allows approximately a 0.4V reduction in the programming control gate voltage and 1V for the erasing control gate voltage. The RTCVD oxides have a cycling endurance out to 1 million cycles. For tunnel dielectrics below 65A, the RTCVD cycling endurance is the same as a thermal oxide. For thicknesses greater than 65A, the RTCVD cycling endurance differs only slightly indicating less positive charge generation and slightly more electron trapping. The charge retention for stressed and unstressed cells with RTCVD tunnel oxides was approximately the same as the thermal oxide tunnel dielectrics. Based on these results, RTCVD oxides are potentially suited for tunnel dielectrics in nonvolatile memory applications where low power and low voltage operations are essential.