High-K Based Non-Volatile Memory Devices with the Light Emitting Application



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The zirconium-doped hafnium oxide (ZrHfO) high-k gate dielectric films with and without the embedded nanocrystals have been studied for the applications of the nonvolatile memory and light emitting devices. By replacing the polycrystalline Si with the novel discrete nanocrystal embedded high-k ZrHfO structure, the promising memory functions can be expected. On the other hand, by using the same metal oxide semiconductor (MOS) capacitor structure with ZrHfO gate dielectric layer but different operating gate voltage (Vg) ranges, e.g., when Vg is larger than the breakdown voltage (VBD), the device starts emitting the white light. This new solid state incandescent light emitting device (SSI-LED) unveils a new concept for the future LED evolution.

The nanocrystals cadmium selenide (nc-CdSe) and molybdenum oxide (nc-MoO3) embedded ZrHfO on the p-type silicon wafer have been fabricated by self-assembly process and studied for their charge trapping, detrapping, and retention characteristics. Moreover, the temperature effect on the memory function has been investigated on the nc-MoO3 embedded device. More than half of the originally trapped holes can be retained in the CdSe nanocrystals for more than 10 years. For the temperature test, with the increase of temperature, the memory window was enlarged and the Coulomb blockade effect was suppressed in the nc-MoO3 embedded ZrHfO memory device. At the same time, the interface quality was deteriorated, the leakage current was increased, and the lifetime was shortened.

The light emission characteristics of the new SSI-LED composed of the ZrHfO or WO3 thin film have been investigated. The light emitting principle is based on the thermal excitation of the conductive paths formed after the dielectric breakdown, which is different from the electron-hole or exciton radiative recombination mechanism in conventional LEDs. The emission spectrum covers the visible to the near IR wavelength range with the color rendering index of 98.4. The light intensity can be enhanced by embedding CdSe nanocrystals into the ZrHfO dielectric layer due to the increase of the defect density which causes the enhancement of the leakage current. The SSI-LED has a very long lifetime of > 5,664 hours in the atmosphere.

Lastly, the additive gas effect of a plasma-based process for etching the copper film over a near-vertical step has been investigated. A new process that minimizes the excessive attacks of the cusp region was developed.