Charge storage in CeO2/Si/CeO2/Si(111) structures by electrostatic force microscopy

Abstract

An electrostatic force microscope was used to write and image localized dots of charge in a double barrier CeO 2 /Si/CeO 2 /Si͑111͒ structure. By applying a relatively large tip voltage and reducing the tip to sample separation to 3-5 nm, charge dots 60-200 nm full width at half maximum of both positive and negative charge have been written. The total stored charge is found to be Q ϭϮ(20-200)e per charge dot. These dots of charge are shown to be stable over periods of time greater than 24 h, with an initial charge decay time constant of ϳ9.5 h followed by a period of much slower decay with Ͼ24 h. The dependence of dot size and total stored charge on various writing parameters such as tip writing bias, tip to sample separation, and write time is examined. © 1999 American Institute of Physics. ͓S0003-6951͑99͒04035-8͔ Cerium oxide (CeO 2 ) is an insulating material with a lattice mismatch of only 0.35% to silicon ͑Si͒ and an energy band gap of ϳ5.5 eV. This attractive set of properties has the potential to lead to a fully functional silicon heterojunction technology. A significant amount of work has been done examining the growth and characterization of CeO 2 crystals on Si, 1-5 and the growth of single crystal Si on to CeO 2 /Si heterostructures 6 has been recently reported. Based on these promising results, a silicon resonant tunneling diode, an improved silicon-on-insulator technology, and stacked silicon electronics have all been proposed. A valuable and interesting addition to this array of technologies would be the capacity for integrated electrostatic data storage.In this letter, we describe the localized charging and subsequent imaging of a double barrier CeO 2 /Si/CeO 2 /Si͑111͒ structure by electrostatic force microscopy ͑EFM͒.7-9 The controllable writing of both positive and negative localized dots of charge with long lifetimes is described and it is further shown that these charge dots may be rewritten and replaced by charge of the opposite sign through the application of an opposite charging bias. A simple analysis is presented to quantify the total amount of charge stored in each charge dot. The time evolution of these charge dots is studied, and charge decay time constants are extracted. Finally, a study is presented of various writing parameters such as tip bias, tip to sample separation, and write time on the size and total stored charge of the resultant charge dots.Samples were produced from commercially available 3 in. Si͑111͒ wafers, n-type with 3.0-4.3 ⍀ cm resistivity. After being subjected to a standard acetone, isopropyl alcohol, deionized water degrease in ultrasound, the wafer was etched in 50:1 HF solution until hydrophobic, rinsed in deionized water, and immediately introduced into vacuum. Electron beam evaporation was used to deposit material from an undoped Si charge and a 99.99% CeO 2 charge to grow the structures. Initially, a 200 Å Si buffer layer was grown and examined by ͑RHEED͒ reflection high-energy electron diffraction to assure the characteristic (7ϫ7) reconstruction was appar...

Quantitative Noncontact Electrostatic Force Imaging of Nanocrystal Polarizability

“…This methodology, with slight variations, has been applied to electric field distributions in devices, 10-12 electrostatics of self-assembled monolayers on surfaces, 13 studies of surface potential variations in oxide bicrystals, 14,15 static and dynamic properties of ferroelectric materials, 16-21 charge measurements in single nanostructures, [22][23][24] as well as observation of charge storage and leakage in various materials. [25][26][27] Although some quantitative measurements of surface charges have been reported, 7,13,22,24-29 most applications of EFM have focused on the mapping of surface potential, which does not require a quantitative understanding of the tip-surface capacitance. However, surface potential does not uniquely determine the charge and polarizability distribution in the sample.…”

Localized charge injection in SiO2 films containing silicon nanocrystals

“…Conducting-tip atomic-force microscopy ͑AFM͒ is sensitive to a variety of forces, including electrostatic, thus making it a good tool for mapping weak electrostatic potentials 4,5 and capacitance 6 on the nanometer scale. It can also be used to inject electrons or holes into a localized region in materials such as polymers, 7 thin insulating films, 8 double-barrier CeO 2 /Si/CeO 2 /Si structures, 9 and Co nanoclusters embedded in SiO 2 . 10 For these reasons, an AFM is a useful tool to study the injection and dissipation of charge in SiO 2 films containing ion-beam-synthesized Si nanocrystals.…”

In situ Raman characterization of CeO2 thin films sputtered on (111) Si in order to optimize the post growth annealing parameters

“…Cubic fluorite CeO 2 has an excellent lattice matching with silicon (misfit factor of 0.35%), so it is expected to be one of the promising buffer layers that combine silicon and various oxides exhibiting superior properties such as high-Tc superconductivity [1,13] or ferroelectricity [14]. Also, due to its relatively high dielectric constant (%26), CeO 2 was known for being a good candidate as the ultra thin gate-insulating layer on Si, which was expected to enable the scaling down of the silicon based devices [15][16][17]. Recently, cerium oxide has drawn a lot of attention, because of its technological importance in catalysis [18].…”