Permittivity enhancement of aluminum oxide thin films with the addition of silver nanoparticles

Abstract

Multilayer reactive electron-beam evaporation of thin aluminum oxide layers with embedded silver nanoparticles ͑Ag-nps͒ has been used to create a dielectric thin film with an enhanced permittivity. The results show a frequency dependent increase of the dielectric constant . Overall stack of the control sample was found to be 7.7-7.4 in the 1 kHz-1 MHz range. This is in comparison with = 16.7-13.0 over the same frequency range in the sample with Ag-nps. ideally suited for use with n-and p-type Si over a range of doping levels. The drawback is that the intermediate dielectric constant of Al 2 O 3 limits the capacitance density compared with other high-dielectrics. It is worth noting at this point that the permittivity of metal nanoparticles has been theorized to be superior to that predicted by the classical electrostatic model. 4 This is explained considering the dipole behavior of nonspherical nanoparticles dispersed in a medium. Each nanoparticle dipole is recognized as behaving like a basic harmonic oscillator or dipole with a relaxation frequency. 5 The deposition of semiconductor device grade films of Al 2 O 3 and HfO 2 on Si is well established. 6,7 However, prior work on using noble metal nanoparticles to increase dielectric constants has focused primarily on polymer and glass dielectrics and processes that are not readily compatible with current integrated circuit fabrication. [8][9][10] Conversely, studies utilizing techniques similar to that used here have not focused explicitly on permittivity enhancement or dielectric properties. 11 The primary differences between the work presented here and earlier works on permittivity enhancement with nanoparticles are the manner in which the silver nanoparticles ͑Ag-nps͒ are deposited, the dielectric medium into which they dispersed, and the deposition and characterization of the film on Si substrates.A control set without Ag-nps and an experimental set with Ag-nps were fabricated. In each set, samples were prepared on both p-and p + -Si ͑100͒ with resistivities of 1-10 and 0.0030-0.00 70 ⍀ cm, respectively. The Si substrates were first cleaned with a modified Shiraki process to remove the native oxide and provide a clean, hydrogen passivated surface. 12,13 After drying under nitrogen, they were immediately transferred to a Kurt J. Lesker AXXIS e-beam evaporation system. From a base pressure of 5 ϫ 10 −7 torr, the substrates were heated to 50°C and oxygen was introduced at 5 SCCM ͑SCCM denotes cubic centimeter per minute at STP͒ and 5 ϫ 10 −5 torr. For control samples without silver, 8.73± 0.08 nm of Al 2 O 3 was then evaporated at 0.5 Å / s. For samples with incorporated Ag-nps, Al 2 O 3 , approximately 3 nm in thickness, was deposited and the chamber was again pumped down to 5 ϫ 10 −7 torr. An ultrathin layer of Ag-nps, about half a nanometer in nominal thickness, was deposited under high vacuum. Oxygen was reintroduced, and approximately 3 nm of Al 2 O 3 was again evaporated. This process was repeated until the film consisted of three layers of Al 2 O 3 with tw...

Hysteresis modeling in graphene field effect transistors

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