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Method for a multilayer tunneling barrier to enhance field emission for programming and erasing

IP.com Disclosure Number: IPCOM000132319D
Publication Date: 2005-Dec-07
Document File: 5 page(s) / 160K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a multilayer tunneling barrier to enhance field emission for programming and erasing. Benefits include improved functionality and improved performance.

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Method for a multilayer tunneling barrier to enhance field emission for programming and erasing

Disclosed is a method for a multilayer tunneling barrier to enhance field emission for programming and erasing. Benefits include improved functionality and improved performance.

Background

              Improved Fowler-Nordheim tunneling (field emission), such as electron or hole tunneling, at a high operational bias voltage is required for efficient program writing or erasing. Also required is a retention-status low operation bias voltage (compared to SiO2).

              Conventionally, flash technology uses a single film SiO2 as a tunneling dielectric material. As it is scaled down in thickness, it develops retention issues due to leakage. Stress induced leakage current (SILC) develops if the SiO2 film is thinner than 8 nm.

              An alternative solution is the single-sided crested barrier. It is a single case of an HfO2 high dielectric constant (high-k) material with a lower band gap on a thin SiO2 layer sandwiched between the HfO2 and silicon (Si).

              Another alternative is a multilayer solution with decreasing energy band gap alignment. This type of structure increases the IV slope and enhances tunneling at high bias and reduces tunneling at low bias in one current direction. However, this solution does not prevent thermal emission noise (see Figure 1).

General description

              The disclosed method includes a multilayer tunneling barrier. For example, a tri-layer tunneling barrier has a center layer with a higher dielectric constant and a lower energy band gap than the surrounding thin barrier layers.

              The key elements of the disclosed method include:

•             Dielectric film with a relatively lower band gap and higher dielectric constant is sandwiched between two or more dielectric layers that have higher band gaps and lower dielectric constant. The surrounding films do not have to be identical and the stack does not have to be symmetrical.

•             At zero or low bias, the conduction band-edge offset or valence band-edge offset of the center layer is greater than the Fermi level of the surrounding electrodes so the tunneling at low bias is effectively dampened by the center layer and the surrounding layers.

•             At high forward or reversed bias, the center film exhibits a limited effect as a barrier to the tunneling so that the enhanced tunneling is achieved.

•             Surrounding films have a sufficient higher energy barrier to effectively prevent thermal emission.

Advantages

              The disclosed method provides advantages, including:
•             Improved functionality due to providing a barrier profile with a low band-gap and high dielectric constant

•             Improved functionality due to enabling the probing of the structure by transmission electron microscope and advanced structure/physical analysis
•             Improved performance due to preventing thermal-emission noise at low bias

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