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RESEARCH GROUP


DR. KIM, Seong-Keun

Smart Electronic Materials Lab

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Dielectric materials for DRAM

The technology road map for dynamic random access memory(DRAM) states that equivalent oxide thickness(tox) less than 0.3 nm is necessary according to a design rule of 1X nm. Reducing the thickness of the dielectric films with k > 40 to achieve the required tox results in unacceptably high leakage currents because of its narrow band gap. Also, down scaling of the DRAM cells to increase packing density has made smaller size capacitors. However, ZrO2 as the commercial dielectric materials with down scaling cannot cover the required capacitance because of its low dielectric constant and high leakage current. Our research group aims to discover the outstanding dielectric materials with high dielectric constant and low leaka ge current for next generation DRAM capacitor.

Select of the dielectric materials
Select of the dielectric materials 이미지

– Almost materials which have high dielectric constant (k > 50) are not useful due to high leakage current by a narrow band gap (3.0–3.2 eV)

Select of the dielectric materials 이미지
Major issue
Poor leakage properties and low dielectric constant
Requirement of the excellent step coverage properties of the dielectric materials (A / R> 100)
Hf-based thin films

Among the various dielectric films, HfO2 thin films have been expected for DRAM capacitor with design rule in ITRS, because of its high dielectric constant and the excellent leakage property since its wide band gap (∼5.8 eV).

Hf-based thin films 이미지
Observe ferroelectricity & Anti-ferroelectricity properties
Addition of Zr, changes the crystal structure of HfO2 thin film.
Forming a HfxZr1-xO2 thin film with high dielectric constant (k > 45)
Ti-based thin films

TiO2 thin film with rutile phase exhibits a k value ~100 and therefore can be used for DRAMs design rule.

Ti-based thin films 이미지
Anatase phase of TiO2 film decrease with increasing O3 feeding time.
Dielectric constant is achieved more than 70 at 3s O3 feeding time.

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