Silicon dioxide SiO 2 has been used as a gate oxide material for decades. As metal-oxide-semiconductor field-effect transistors MOSFETs have decreased in size, the thickness of the silicon dioxide gate dielectric has steadily decreased to increase the gate capacitance and thereby drive current, raising device performance.
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As the thickness scales below 2 nm , leakage currents due to tunneling increase drastically, leading to high power consumption and reduced device reliability. Ignoring quantum mechanical and depletion effects from the Si substrate and gate, the capacitance C of this parallel plate capacitor is given by. In such a scenario, a thicker gate oxide layer might be used which can reduce the leakage current flowing through the structure as well as improving the gate dielectric reliability.
High Permittivity Gate Dielectric Materials Springer Series in Advanced Microelectronics
See the industry roadmap,  which limits threshold to mV, and Roy et al. Thus, according to this simplified list of factors, an increased I D,sat requires a reduction in the channel length or an increase in the gate dielectric capacitance.
Replacing the silicon dioxide gate dielectric with another material adds complexity to the manufacturing process. Silicon dioxide can be formed by oxidizing the underlying silicon, ensuring a uniform, conformal oxide and high interface quality.
As a consequence, development efforts have focused on finding a material with a requisitely high dielectric constant that can be easily integrated into a manufacturing process. Materials which have received considerable attention are hafnium silicate , zirconium silicate , hafnium dioxide and zirconium dioxide , typically deposited using atomic layer deposition. It is expected that defect states in the high-k dielectric can influence its electrical properties.
Defect states can be measured for example by using zero-bias thermally stimulated current, zero-temperature-gradient zero-bias thermally stimulated current spectroscopy ,   or inelastic electron tunneling spectroscopy IETS. The industry has employed oxynitride gate dielectrics since the s, wherein a conventionally formed silicon oxide dielectric is infused with a small amount of nitrogen.
The nitride content subtly raises the dielectric constant and is thought to offer other advantages, such as resistance against dopant diffusion through the gate dielectric. This helped drive cost-effective implementation of semiconductor memory , starting with nm node DRAM.
In early , Intel announced the deployment of hafnium -based high-k dielectrics in conjunction with a metallic gate for components built on 45 nanometer technologies, and has shipped it in the processor series codenamed Penryn. While not identified, the most likely dielectric used in such applications are some form of nitrided hafnium silicates HfSiON.
HfO 2 and HfSiO are susceptible to crystallization during dopant activation annealing. This leakage effect becomes more severe as hafnium concentration increases.
There is no guarantee however, that hafnium will serve as a de facto basis for future high-k dielectrics. The ITRS roadmap predicted the implementation of high-k materials to be commonplace in the industry by From Wikipedia, the free encyclopedia.
Redirected from High-k dielectric. Electronics portal. International Technology Roadmap for Semiconductors: Update.
Archived from the original PDF on McGraw-Hill Professional. Applied Physics Letters. Bibcode : ApPhL..