High Resolution Electron Beam Research Articles

Fabrication and performance of 50 nm T-gates for InP high electron mobility transistors

Fifty nanometre gate length T-gates In0.52A10.48As/In0.53Ga0.47As high electron mobility transistors (HEMTs) on a InP substrate were fabricated with high resolution electron-beam (e-beam) lithography using a novel UVIII/LOR/PMMA T-gate resist stack and with a non-selective digital wet etch gate recess technology. The reproducibility of the gate lithography depends on the substrate slope when mounted on the holder of e-beam lithography tool. This mounting effect is almost eliminated by calibrating the tool using a specially fabricated marker on the wafer instead of the holder marker as in usual. Initial devices exhibited a maximum transconductance (gm) of 950 mS/mm and a current cut-off frequency (ft) of 300 GHz.

Exploring the high sensitivity of SU-8 resist for high resolution electron beam patterning

We have explored the feasibility of using negative epoxy novolak-based SU-8 2002 resist as an electron beam lithography resist for ultra high speed fabrication of large areas of high resolution patterns. 75 nm-wide lines have been obtained in thin-layered SU-8 films, using a 50 keV electron beam system, and the required exposure dose was found to be around 3.6 μC/cm2, which is more than 100 times less than that of commonly used polymethyl methacrylate resist (typically 500 μC/cm2). Therefore, mass production of large areas of nanostructures should be possible for a number of applications.

Nanoelectrode-based devices for electrical biodetection in liquid solution

The fabrication of nanosystems for the electrical detection of biomolecular interactions is reported. Using a planar process on silicon involving high-resolution electron beam lithography and lift-off, we have demonstrated the reliable fabrication of nanoelectrode-based devices with controlled gap dimensions ranging from 100 nm down to 20 nm. These devices were used to achieve the electrical detection of gold colloids. We show that binding events can occur in inter-electrode gaps, leading to a drastic modification of the electrical transport through the nanojunction. Using a similar approach, electrical measurements in solution were performed by developing Poly(dimetylsiloxane) molded microtanks. First experiments involving gold colloids in solution have shown the possibility of detecting individual nanoparticles. The versatility and the very high sensitivity of these devices added to the simplicity of implementation make this approach very attractive for the fabrication of efficient nanobiosensors.

Nanodevices for correlated electrical transport and structural investigation of individual carbon nanotubes

We report a new approach to the correlation of the structural properties and the transport properties of carbon nanotubes. Through an original combination of UV lithography, custom-made photosensitive sol–gel resist and deep reactive ion etching (RIE), we have successfully integrated membrane technology and nanodevice fabrication for the electrical connection of individual carbon nanotubes. After single wall nanotube (SWNT) deposition by molecular combing and contacting using high resolution electron beam lithography, we obtain a device that allows both the investigation of the nanotubes and the contact regions by transmission electron microscopy (TEM) and the measurement of the electronic transport properties of the same individual nano-object. The whole fabrication process is detailed and the demonstration that the micro membranes are suitable for both TEM inspection and nanoelectrode fabrication is given.

Nanoelectrode-based devices for electrical biodetection in liquid solution

The fabrication of nanosystems for the electrical detection of biomolecular interactions is reported. Using a planar process on silicon involving high-resolution electron beam lithography and lift-off, we have demonstrated the reliable fabrication of nanoelectrode-based devices with controlled gap dimensions ranging from 100 nm down to 20 nm. These devices were used to achieve the electrical detection of gold colloids. We show that binding events can occur in inter-electrode gaps, leading to a drastic modification of the electrical transport through the nanojunction. Using a similar approach, electrical measurements in solution were performed by developing Poly(dimetylsiloxane) molded microtanks. First experiments involving gold colloids in solution have shown the possibility of detecting individual nanoparticles. The versatility and the very high sensitivity of these devices added to the simplicity of implementation make this approach very attractive for the fabrication of efficient nanobiosensors.

Fabrication and performance of 50 nm T-gates for InP high electron mobility transistors

Fifty nanometre gate length T-gates In 0.52A1 0.48As/In 0.53Ga 0.47As high electron mobility transistors (HEMTs) on a InP substrate were fabricated with high resolution electron-beam (e-beam) lithography using a novel UVIII/LOR/PMMA T-gate resist stack and with a non-selective digital wet etch gate recess technology. The reproducibility of the gate lithography depends on the substrate slope when mounted on the holder of e-beam lithography tool. This mounting effect is almost eliminated by calibrating the tool using a specially fabricated marker on the wafer instead of the holder marker as in usual. Initial devices exhibited a maximum transconductance ( g m) of 950 mS/mm and a current cut-off frequency ( f t) of 300 GHz.

Fabrication of nanodevices for magneto-transport measurements through nanoparticles

We are developing nanoelectrodes for investigation of magneto-transport mechanisms through a single or a few nanoparticles. In this work, we present two different ways for patterning these nanodevices, based on high resolution electron beam lithography (HREBL). The first method consists in defining electrode shape patterns in a positive PMMA resist layer by HREBL and then lifting-off a metallic or ferromagnetic film deposited by ion beam assisted evaporation. The second method consists in etching a continuous metallic or ferromagnetic thin layer deposited by sputtering, using as etching mask a negative PMMA resist previously patterned by HREBL. The entire processes are described in detail and the geometrical quality and resolution of the nanoelectrodes obtained in each case are analysed and compared by scanning electron microscopy.

Exploring the high sensitivity of SU-8 resist for high resolution electron beam patterning

We have explored the feasibility of using negative epoxy novolak-based SU-8 2002 resist as an electron beam lithography resist for ultra high speed fabrication of large areas of high resolution patterns. 75 nm-wide lines have been obtained in thin-layered SU-8 films, using a 50 keV electron beam system, and the required exposure dose was found to be around 3.6 μC/cm 2, which is more than 100 times less than that of commonly used polymethyl methacrylate resist (typically 500 μC/cm 2). Therefore, mass production of large areas of nanostructures should be possible for a number of applications.

Feasibility of dynamic high resolution electron beam computed tomography for diagnosing bronchiolitis obliterans syndrome (BOS) in lung transplant recipients

Feasibility of dynamic high resolution electron beam computed tomography for diagnosing bronchiolitis obliterans syndrome (BOS) in lung transplant recipients

Electron-beam-induced reactivation of Si dopants in hydrogenated two-dimensional AlGaAsheterostructures: a possible new route for III–V nanostructure fabrication

Hydrogen incorporation in n-type Si-doped GaAs epilayers is a well-known process whichleads to the neutralization of the active Si impurities with the formation of SiH complexes.Recently, we have shown that SiH complex dissociation and, consequently, Si-dopantreactivation could occur when the epilayers are exposed to an electron beam.Two epilayers have been studied: the first is a0.35 µm thick hydrogenated Si-doped GaAs epilayer and the second is Si planar-dopedAlGaAs/GaAs/InGaAs heterostructures.Firstly, Hall effect measurements have been carried out on the epilayers exposed, after RFhydrogen plasma exposition, to increasing electron doses with different injectionenergies. For the 2D heterostructures, we have observed that the free carrier densityNs does notvary significantly for weak electron densities. This reactivation presents a threshold value, contrary to the0.35 µm epilayerin which Ns varies quite linearly. It will be shown that such phenomena might be attributed to thefilling of surface states as the dopants are progressively reactivated.Then, using a high spatial resolution electron beam lithography system, nanometricconductive patterns have been fabricated starting from hydrogenated epilayers. Electricmeasurements have been performed and the results obtained show that about 15 nm spatialresolution could be expected.In conclusion, taking into account this spatial resolution, the high spatial contrast ofconductivity which could be expected due to the existence of an electron dosethreshold, and the high mobility of the AlGaAs/GaAs/InGaAs heterostructure,the effects described in this paper could open a new way for the fabrication ofIII–V 1D or 2D mesoscopic structures for electronic or optoelectronic applications.

Fabrication of ultrashort T gates using a PMMA/LOR/UVIII resist stack

In this article, we report a procedure for the fabrication of ultrashort T gates using high resolution electron beam lithography and a PMMA/LOR/UVIII resist stack. The intermediate lift-off resist (LOR) layer improves the quality of gate lithography, and consequently, device yields. It is unaffected by wet chemical gate recessing procedures and we report the application of the procedure to the fabrication of pseudomorphic and metamorphic high electron mobility transistors (pHEMTs) with 50 nm T gates. Fabricated pHEMTs had a gm of 600 mS/mm and ft of 200 GHz. Metamorphic HEMTs had a gm of 1500 mS/mm and ft of 350 GHz. We believe these are the fastest transistors of their kind in the world.

Electrical characterization of InGaN quantum well p–n heterostructures

In this work, two methods for electrical characterization of InGaN quantum well p–n heterostructures at the nanometer level are presented. Cross-sectional Electrical Force Microscopy and High Resolution Electron Beam Induced Current (HR-EBIC) are used to study and identify regions of the cross-sectional surface of InGaN heterostructures with different types of electrical conductivity, the location of the InGaN quantum well, the location of the p–n junction, and the depletion layer. HR-EBIC was implemented in a Scanning Transmission Electron Microscope to take advantage of the high resolution chemical imaging capabilities of this microscope, such as Z-Contrast and Energy Dispersive X-ray Spectroscopy, and the small spread of the high energy electron beam in the electron transparent thin sample that allows electron beam induced current imaging with nanometer resolution.

Silicon single-electron parametron cell for solid-state quantum information processing

We present the fabrication and preliminary electrical characteristics of a parametron cell, consisting of two conducting islands separated by a very short nanowire, with an integrated capacitively coupled electrometer and gates, fabricated using a trench-isolated structure on silicon-on-insulator material using high-resolution electron beam lithography and reactive-ion-etching. The structure is modified in comparison to previously presented devices, such that both the parametron island sizes and the inter-island separation have been reduced in order that single-electron effects influence the polarisation of the cell. This polarisation is used in order to achieve classical computation by the application of appropriate pulses on the gates.

Alignment and nano-connections of isolated carbon nanotubes

We report a new approach for the alignment and the electrical nano-connection of isolated carbon nanotubes (CNTs). Through a novel combination of proven technics, we have been able to align isolated carbon nanotubes and selectively contact those CNTs by high resolution electron beam lithography (HREBL). Resistance versus temperature (R(T)) experiments have been carried out to determine the reliability of the metal–CNTs interface and to probe the electronic conductance of the CNT.

三次元磁界測定装置を用いた磁気ヘッド評価

We analyzed magnetic field distributions of two kinds of write heads, using a modified high-resolution electron beam tomography technique which employs a patterned electron beam. The heads differ in their saturated magnetic flux density of upper poles, overwrite properties, and resolutions. As a result, we confirmed that the write component of the magnetic field affected the overwrite properties and the magnetic component perpendicular to the air bearing surface affected the resolutions.

Evaluation of calixarene—derivatives as high-resolution negative tone electron-beam resists

We present a systematic evaluation of calixarene derivatives as high-resolution negative tone resists for electron-beam lithography with a focus on their sensitivities. We studied the effect of a modification of the calixarene molecules to trimethysilyl ethers as well as the effect of an introduction of an allyl group and showed that the introduction of double bonds into the molecules can improve the sensitivity of the resists while their position does not seem to be important. The high-resolution capability of tetraallylcalix[4]arene was confirmed by fabricating an 18 nm dot array.

Fabrication of high electron mobility transistors with T-gates by nanoimprint lithography

T-gates are commonly used in high frequency low noise transistors on III–V materials since they provide a combination of short gate length and low gate resistance. Nanoimprint lithography can produce minimum pattern feature sizes equivalent to those attainable by high resolution electron beam lithography and it has potential advantages in terms of speed and cost. The imprint lithography step must be reliable and compatible with existing device process flows. In this article we describe a bilayer resist imprinting procedure for the fabrication of 120 nm T-gates for high electron mobility transistors. The results of transistor dc characterization are also presented and are similar to those obtained for transistors fabricated on the same material with gates realized by electron beam lithography.

Single-electron parametron memory cell

A single-electron parametron memory cell, based on two conducting islands separated by a multiple tunnel junction, has been realized in highly doped silicon-on-insulator. A memory cell with integrated read-out electrometers was fabricated using a combination of high-resolution electron beam lithography and reactive ion etching. The layout and operation of the memory cell is based on a proposal by Korotkov and Likharev, but modified in order to simplify fabrication. The operation of the electrometer, and the cell polarization characteristics are investigated by low temperature electrical measurements. Memory operation is indicated by current hysteresis in the electrometer characteristics with appropriate gate bias voltages.

Field emission from individual multiwalled carbon nanotubes prepared in an electron microscope

Individual multiwalled carbon nanotube field emitters were prepared in a scanning electron microscope. The angular current density, energy spectra, and the emission stability of the field-emitted electrons were measured. An estimate of the electron source brightness was extracted from the measurements. The results show that carbon nanotubes are promising candidates to replace existing sources in high-resolution electron beam instruments.

Adhesive forces investigation on a silicon tip by contact-mode atomic force microscope

An atomic force microscope operating in contact mode is used in this letter for probing the adhesive forces at the apex of a silicon nanotip with typical radius smaller than 15 nm, fabricated using a combination of high-resolution electron beam lithography and plasma dry etching. The amplitude of the forces is deduced from force versus distance curve measurements. By determining the contact point and the pull-off force from the force curves, the surface topography and the adhesive forces are simultaneously obtained at various locations on the surface. This letter reports both measurements and modeling of adhesive forces versus the contact point on the nanotip. As the nanotip is sharper and has a smaller aperture angle than the employed atomic force microscope tip, the measurements are focused on the nanotip apex.