Ivan Maximov

Improving stamps for 10 nm level wafer scale nanoimprint lithography

The smaller the features on the stamp the more important are the interactions between stamp and polymer layer. A stamp rich in small structures will effectively show a surface area enlargement, which generally leads to adhesion of the polymer to the stamp. This makes a subsequent imprint impossible without troublesome and time-consuming cleaning. The anti-adhesion properties of Si- or SiO2-based stamps can be improved by binding fluorinated silanes covalently to the surface. In this paper, we demonstrate that the deposition procedure as well as the environment during deposition are important with respect to the quality and performance of the molecular layer

Nanoimprint lithography at the 6 in. wafer scale

We demonstrate the nanoimprint lithography (NIL) technique with sub 100 nm resolution, on 6 in. Si substrates. The pattern transfer is performed using a specially designed NIL machine optimized to achieve a very high degree of parallelism between stamp and substrate. The stamp is made with the help of electron beam lithography and Ni electroplating achieving features below 100 nm in size. The nanoimprint process is done in a single layer as well as in a multilayer resist scheme with subsequent O2-plasma etching and metal lift-off.

Sulfur passivation for ohmic contact formation to InAs nanowires

We have studied the formation of ohmic contacts to InAs nanowires by chemical etching and passivation of the contact areas in an ammonium polysulfide, (NH4)2Sx, water solution. The nanowires were exposed to different dilution levels of the (NH4)2Sx solution before contact metal evaporation. A process based on a highly diluted (NH4)2Sx solution was found to be self-terminating, with minimal etching of the InAs. The stability of the contacts was investigated with electrical measurements as a function of storage time in vacuum and air.

Nonlinear operation of GaInAs/InP-based three-terminal ballistic junctions

We report on nonlinear electrical properties of three-terminal ballistic junctions (TBJs) based on high-electron-mobility GaInAs/InP quantum-well structures. Nonlinear electrical transport behavior of the TBJs is found, and we show a correlation between this behavior and the linear regime of electron transmission in the devices. We also study device geometry effects on these electrical properties of the TBJs. Finally, we demonstrate room-temperature operation of the devices. The results obtained are compared with recent predictions by Xu [H. Q. Xu, Appl. Phys. Lett. 78, 2064 (2001)] and good agreement is found.

Assembling strained InAs islands on patterned GaAs substrates with chemical beam epitaxy

The assembly of strained InAs islands was manipulated through growth on patterned GaAs substrates with chemical beam epitaxy. Conditions were found to selectively place the islands in patterns features but not on surrounding unpatterned fields. Chains of islands having 33 nm minimum periods were formed in trenches, and single or few islands were grown in arrays of holes. When capped with GaAs, the islands behave as quantum dots and are optically active.

Large scale nanolithography using nanoimprint lithography

Nanoimprint lithography is a promising technique for fabrication of nanometer-sized structures with an eventual throughput capacity similar to UV-lithography based production of integrated circuits. In this article we address the possibility for wafer scale nanoimprint lithography, and the results presented here are all obtained from 2 in. sized substrate and stamp wafers. Our nanoimprint lithography equipment is described and some of its characteristics are discussed. These include ultrafast imprint cycle times of less than 2 min, good temperature monitoring, and control possibility of the substrate temperature. We show complete results after imprint, removal of remaining resist, and liftoff for 2 in. wafers. Furthermore, in this article the relation between polymer sticking to the stamp applied pressure, stamp depth, etc. is studied in detail.

A novel frequency-multiplication device based on three-terminal ballistic junction

In this letter, a novel frequency-multiplication device based on a three-terminal ballistic junction is proposed and demonstrated. A 100 nm-size, three-terminal ballistic junction and a one-dimensional (1D), lateral-field-effect transistor with trench gate-channel insulation are fabricated from high-electron-mobility GaInAs/InP quantum-well material as a single device. The devices show frequency doubling and gain at room temperature. The performance of these devices up to room temperature originates from the nature of the device functionality and the fact that the three-terminal device extensions are maintained below the carrier mean-free path. Furthermore, it is expected that the device performance can be extended up to THz-range.

Fabrication of Si-based nanoimprint stamps with sub-20 nm features

We present two alternative methods for fabrication of nanoimprint lithography stamps in SiO2 with sub-20 nm features: (a) optimized electron beam lithography (EBL) and lift-off patterning of a 15-nm thick Cr mask, and (b) aerosol deposition of W particles in the 20-nm size range. In both cases, the pattern transfer into SiO2 was performed using reactive ion etching (RIE) with CHF3 as etch gas. In the first approach, we used a double layer resist system (PMMA/ZEP 520A7 positive resists) for the EBL exposure. Resist thickness, exposure dose and development time were optimized to obtain 15-20 nm features after Cr lift-off. In the second approach, we used size selected W aerosol particles as etch masks during etching of SiO2. Both methods of stamp fabrication are compared and discussed

Nanoimprint- and UV-lithography: Mix&Match process for fabrication of interdigitated nanobiosensors

A complete nanobiosensor structure consisting of a 200 @mm x 200 @mm area containing 100 nm sized interdigitated nanoelectrodes with varied interelectrode distances has been fabricated using nanoimprint lithography (NIL) in combination with UV-lithography. The complete structure has been characterized with admittance spectroscopy. In the paper are discussed the needs and key issues for nanosensors and the capability offered by using NIL for fabrication of such sensors.

Electrical properties of self-assembled branched InAs nanowire junctions

We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.