Ion Beam Etching Technique Research Articles

Trimming of step-edge junctions for improvement of SQUID performance

We have applied an Ar ion beam etching technique to trim the critical current, Ic, and the normal resistance, Rn, of step-edge Josephson junctions which provides a means to optimize SQUID performance. By using this technique, Ic can be reduced by more than one order of magnitude and Rn can be increased to over 10 Ω. Significant improvements in SQUID performance have been demonstrated with this technique. White noise of 80 f T Hz−1/2 was achieved from a trimmed 5 mm dc SQUID that had poor initial performance.This paper was presented at the 8th International Superconductive Electronics Conference, Osaka, Japan, 19–22 June 2001.

Magnetization reversal of a multilayered FeGd dot array imaged by transmission x-ray microscopy

The magnetization reversal of an array of 1 μm squared FeGd dots has been studied by magnetic transmission x-ray microscopy (MTXM). A (4 Å Fe/4Å Gd)×75 multilayered FeGd system has been prepared on a 30 nm thin Si3N4 membrane by sputtering and structured by optical lithography and ion beam etching techniques. Both the domain structure within each single dot and the collective switching behavior could be observed with MTXM. A large variation in the nucleation field of the dots was found and can be attributed to the shape of the dots. A correlation between the nucleation field and the perimeter of each dot could be deduced. Hysteresis loops of individual dots are derived, taking into account the proportionality of the dichroic contrast to the magnetization of the sample. The stepped profile of the magnetization loop of a single dot is found to be clearly distinct from a continuous film. The high lateral resolution and the possibility to record the images in varying external magnetic fields proves that MTXM is a highly adapted tool to investigate nanostructured magnetic systems.

Anwendung des lonenstrahlätzens bei Schichtverbundwerkstoffen/ The Use of Ion Beam Etching in Composite Layered Materials/

Ion beam etching is used to develop the structure of thermally sprayed layers of a number of different combinations of materials. These layers may consist of steel together with various additives, electrolytic copper or special metals, which are applied to substrate materials such as unalloyed or high-alloyed steels, grey cast iron or titanium. In order to evaluate the applicability of this type of etching technique for the use of different composite systems, the results of ion beam etching are compared with those obtained by using a number of standard chemical etching techniques. In the chemical or electrochemical etching of composite materials the potential differences between the different phases present are extremely important. In ion beam etching, among other factors, the sputtering yield (S) plays an essential role. For determining the quality of the layer/substrate interface in particular, ion beam etching is superior to chemical etching. In the first part of this paper, thermally sprayed layers of steel containing NiCrSiB and of a mixed metal containing steel and SnBz6 on an unalloyed steel substrate (Ck15) are investigated. They are etched both chemically and using ion beam etching technique. The results obtained are compared and supported by means of EDX-analysis.

Diamond-like carbon films prepared by filtered arc deposition for electron field emission application

In this paper, hydrogen-free diamond-like carbon (DLC) films were prepared by filtered arc deposition. The effect of sp 3 content and annealing on electron field emission properties of the DLC films was studied. A patterned DLC flat thin film column emitter array was fabricated by oxygen reactive ion beam etching (RIBE) technique. It was shown that the threshold field of the DLC films was approximately 3–15 V/μm. Field emission site density ranged from 5×10 2 to 2×10 3 /cm 2. The field emission mechanism of the DLC films is also discussed.

Inductance matching of high- TC dc-SQUIDs in planar gradiometers using a laser patterning technique

The inductance of the dc-SQUID in a planar galvanically coupled gradiometer of YBa 2Cu 3O 7− x was changed by lengthening the SQUID loop with a focused laser beam. The dc-SQUID inductance was increased from 50 pH to values close to 300 pH by this technique. This increased SQUID inductance changed the effective area of the gradiometer device as well as the SQUID parameter β L. We focused our investigations on the change of the peak-to-peak voltage of the SQUID modulation, on the change of the white noise properties as well as on the change in low frequency noise depending on an effective area and SQUID parameter β L. Different fixed critical currents of the dc-SQUID were considered in order to determine their influence on SQUID operation. For critical currents below 200 μA, a maximum of the white field gradient resolution could be achieved for corresponding SQUID parameters β L between 1.5 and 6 with 340 fT/(cm Hz 1/2) as the lowest noise level. Here, the necessity of a high I C R N product, an optimum critical current and an optimum dc-SQUID inductance was shown in order to realize a high device sensitivity. The influence of the grain boundary angle to achieve a high field gradient resolution even in unshielded environment as well as the combination of the increase of SQUID inductance with an additional ion beam etching technique for critical current reduction is considered.

Investigation of advanced position error signal patterns in patterned media

A potential approach to extending current thin film media to 100 Gbits/in2 recording density is physical patterning of the media, perhaps via an etching technique. An advantage of patterning is the capability of creating advanced position error signal (PES) patterns that are difficult or impossible to generate with writing by a recording head. This study uses spin stand tester to investigate various PES patterns generated by a focused ion beam etching technique on conventional thin film disks. For all practical purposes, the patterned PES eliminates transition noise, track edge noise, and erase band, therefore, demonstrates a much better PES signal than conventionally written servo patterns.

InGaN/GaN multi-quantum well distributed Bragg reflector laser diode

An electrically injected InGaN/GaN-based distributed Bragg reflector (DBR) laser was demonstrated. Surface grating was formed on both sides of ridge waveguide by chemically assisted ion beam etching technique. The observed threshold current was 375 mA with threshold voltage of 15.1 V for 500×3 μm2 devices. The emission of the DBR laser occurred in a single longitudinal mode at a wavelength of 401.3 nm. The ratio of sidemode suppression was found to be more than 13 dB until a current injection of 1 A.

Fabrication of Silicon-Blazed Gratings for Couplers

To our knowledge, no blazed grating has been fabricated in silicon (Si) at a pitch of less than half a micron. In this article, we report the fabrication of Si-blazed gratings at the period of 400 nm, using electron beam lithography and ion beam etching techniques. The blazed grating is extremely useful as a grating coupler in integrated optics, operating at the telecommunication wavelength of 1.3 mum, because very high output efficiency of the grating coupler is expected. This will allow coupling to thin film devices in silicon, previously not regarded as promising because coupling to them was very inefficient.

Recording, noise, and servo characteristics of patterned thin film media

In this paper, we present a combined experimental and micromagnetic simulation study of the recording, noise and position error signal characteristics in patterned thin film media. The medium is patterned with a focused ion beam etching technique on typical present thin film disks. It is found the transition noise is completely absent in the patterned thin film media. Comparing with continuous thin film media, the medium noise is reduced to the level of noise at saturation remnant state and is no longer density-dependent. With the elimination of transition noise, the signal-to-medium-noise ratio will be sufficient at very narrow track widths without further reduction of grain size. A slight increase of intergranular exchange coupling will have little impact on medium noise, but enhance thermal magnetic stability of the medium. Down track orientation of the crystalline easy axes will further improve the recording performances. Position error signal patterns in patterned media can be more versatile and significantly more effective and efficient.

Electron field emission from a patterned diamond-like carbon flat thin film using a Ti interfacial layer

A 200-nm-thick diamond-like carbon film was prepared on Ti-deposited Si (ρ<0.01 Ω cm) using a filtered arc deposition technique. Field-emission properties of it are enhanced as compared to films deposited on Si, showing an increased current and emission site density (∼1.2×103/cm2). A patterned diamond-like carbon flat thin film on Ti-deposited Si fabricated by the oxygen reactive ion-beam etching technique shows further enhanced field-emission properties. An emission site density of 3×103/cm2 was obtained. Field emission could be observed at a field value as low as 2.1 V/μm. It is shown that the low potential barrier at the interface and high local geometric electric field enhancement around the edges produced by reactive ion-beam etching are possible causes for the enhanced effects. It can also be explained by the Geis’ metal–diamond–vacuum triple junction emission mechanism.

Focused Ion Beam Process for Formation of a Metal/Insulator/Metal Double Tunnel Junction

An improved method to fabricate a small lateral double tunnel junction which utilizes focused ion beam (FIB) etching and lift-off techniques is proposed. A double layer resist consisting of nitrocellulose and germanium layers was used. Narrow grooves with widths comparable to or narrower than the FIB diameter were formed in a ferromagnetic layer of Ni, and Ni/Ni-oxide/Au/Ni-oxide/Ni and Al/Al-oxide/Ni/Al-oxide/Al double junction structures were fabricated using the proposed method. The measured voltage and current characteristics of the latter structures indicated that double tunnel junctions with a barrier height of 0.61 eV were fabricated and suggest that this is a promising method to fabricate island structures for devices utilizing Coulomb blockade or spin blockade effects.

Self-aligned formation of a vertical-type micro field emitter with a volcano-shaped gate electrode protruding towards the cathode by focused ion-beam sputter etching and deposition

A vertical-type micro field emitter with a volcano-shaped gate electrode protruding towards the cathode was fabricated by the focused ion-beam sputter etching and deposition technique. Chromium was deposited on the silicon dioxide layer grown on the silicon substrate and patterned to be a band with width of 5 µm and length of 20 µm. After patterning, the oxide layer below the chromium film was etched away with hydrofluoric acid, resulting in the formation of a chromium bridge. This bridge, together with the silicon substrate, was machined by a circularly-deflected focused ion beam to make a ring-shaped erosion, leaving a small protrusion at the center. Simultaneously, sputtered silicon was deposited to the edge of the gate electrode to form a protrusion like a volcano. Formation of this protruding gate electrode was confirmed by a Monte Carlo simulation. This technique has a unique character, such that the depositing material is supplied from the back side, and may be applicable to fabrication of micromachines and so on.

Reactive Ion Beam Etching (RIBE) Technique and Instrumentation for SEM Specimen Preparation of Semiconductors

Argon ion beam etching has established itself as an alternative technique to “wet chemical” etching for the preparation of cross sectional SEM specimens of semiconductors [1]. Complementing this technique, we are reporting the results of an iodine RIBE method for improved etching/cleaning capabilities with a measurable increase in etching rates as compared to argon ion beam etching. RIBE systems have been used for decades in the semiconductor research/industry for wafer processing, patterning and surface cleaning. This same technique has also been used for high quality TEM specimen preparation of certain semiconductor materials [2,3]. The beneficial aspects of the iodide RIBE technique for surface etching for a variety of semiconductor structures along with the related instrumentation will be discussed. The semiconductor specimens include traditional ICs and more advanced copper technology devices.The design and construction of the original system used in this work has already been reported [4].

Fabrication and characterisation of YBCO single grain boundary step edge junctions

We use ion beam etching techniques to fabricate YBCO step edge junctions (SEJ) on MgO substrates. Argon ion-beam etching (IBE) of the substrate at angles other than at normal incidence is used to define the step height and angle. Thin (/spl sim/300 nm) magnetron sputtered YBCO films are deposited over the step and patterned using microlithography and cold substrate ion-beam etching techniques. The critical current, I/sub c/ of these SEJs can be controlled by varying the angle of the step etched into the substrate. Fabrication techniques are described which produce one grain boundary at the top of the step and include a smooth return path thereby avoiding a second grain boundary at the bottom of the step. At 77 K, the current-voltage (I-V) characteristics show resistively shunted junction behaviour. These junctions routinely demonstrate reasonably large I/sub C/R/sub N/ products (0.1-0.6 mV), making them suitable for applications in high temperature SQUID devices.

Three-dimensional micro-structures for the embedding of living cells

AFM (atomic-force microscope) studies of living cells have been of considerable interest since the invention of the technique itself. However, due to the strong interaction between tip and the soft cell the latter one can get damaged. In this work, we report the fabrication of three-dimensional structures on the basis of Si/SiO2 and quartz/SiO2/SixNy with e-beam lithography (EBL), reactive ion beam etching (RIBE) and different wet etching techniques for the embedding of living cells and the stabilization of the cell membrane. All developed structures contain: (1) a cavity with the size of the mature cell, (2) at least one opening large enough for the insertion of the immature cell in suspension and (3) a covering structure confining enough to hinder the mature cell from any movement and to immobilize the cell membrane. Different three dimensional structures have been utilized to culture living cells and to study them in a physiological environment.

Fabrication method for multiple wavelength vertical-cavity emitter arrays by SiNx layer thickness control

We report very narrow and equally spaced eight-channel multiple-wavelength vertical-cavity emitter arrays emitting from 855 to 862 nm with the average spacing of 0.91 nm. For the postgrowth wavelength adjustment, a binary-coded multistep ion beam etching technique is applied to control the thickness of a SiN/sub x/ tuning layer located on the first Al/sub 0.15/Ga/sub 0.85/As quarter-wave layer above the active region. Our result indicates the possibility of the precisely spaced vertical-cavity surface-emitting laser arrays using this kind of postgrowth wavelength adjustment technique.

Linear high-Tc YBa2Cu3O7-δ superconducting thin film infrared detectors coupled with a cylindrical microlens array in quartz glass substrate

Monolithic linear cylindrical microlens array in a quartz glass substrate is fabricated using photolithography and ion beam etching technique, the high-Tc YBa2Cu3O7−δ superconducting thin films are deposited through excimer laser scanning ablation, the superconducting thin films are patterned by photolithographic method and ion beam etching technique, and the hybrid structure of the microlens array component and the superconducting IR detectors has been obtained using an IR glue to cement the microlens component onto the superconducting device. We also investigate the optical response characteristics of the hybrid device in the optical spectral region of 1 ~ 5 μm, as follows. The average optical responsivity \((\overline R )\) of the hybrid device is 1.6×104 V/W, average noise equivalent power \((\overline {NEP} \;)\) is 2.3×10−12 WHz−1/2, average detectvity \((\overline {D^ * } )\) is 3.2×109 cmHz1/2W−1, and the non-uniformity of detectvity (D*) is not more than 14%. The experimental results show that the performance of the superconducting device is improved notably using a quartz glass refractive microlens array as the incident IR radiation concentrators.

HTSC devices fabricated by selective epitaxial growth

The use of a selective epitaxial growth technique for fabricating YBCO thin-film microstructures is described. No film post-deposition processing is required; hence damage to the structure is minimized. The technique is compatible with a passivation process to protect the structure without exposure to air. The microbridges, Josephson junctions and rf SQUIDs protected by an amorphous YBCO passivation have long lifetime even after severe accelerated aging tests. Rf SQUIDs fabricated by this technique show a significant reduction of low-frequency noise when operating in weak magnetic fields compared with SQUIDs fabricated by the conventional ion beam etching technique.

Optimization of etching parameters of a fluorinated polyimide using the RIBE technique

A parametric study of etching a new type of fluorinated polyimide (6FDA-ODA) has been carried out. This kind of material was especially elaborated for plasma etching (reactive ion etching, RIE); its behaviour was tested with the reactive ion beam etching (RIBE) technique which uses an (O + ) reactive ion beam and allows independent control of the ion energy and current density of the beam. Etch rates were measured as a function of energy (E), current density (J) and incident angle (θ) of the beam with the sample normal. These rates were shown to present a maximum value (1000 A min -1 ) for an energy flux of about 3 W cm -2 ) (E = 6keV and J = 0.5 mA cm -2 ) and decreased when 9 increased. These results were then compared with etching rates obtained with chemically inert ions (Ar + ): in this case, etching rates were five times lower than those measured with O + ions.

Materialographische Gefügeentwicklung durch Anwendung des Ionenstrahlätzens / Use of ion beam etching for producing topographical microstructure

Selective ion beam etching (IBE) is a particularly suitable method for revealing the microstructures of heterogeneous materials, composites and chemical resistant materials, as the individual phases of these materials can often be either chemically quite different or covered with protective layers which prevent them from being etched conventionally, either chemically or electrochemically. The results of etching both composites and compounds using both ion beam and chemical etching techniques were compared and discussed. The microstructures revealed were assessed using Optical Light Microscopy, Scanning Electron Microscopy (SEM), Scanning Tunnel Microscopy (STM) and Atomic Force Microscopy (AFM).