摘要:

We have fabricated and electrically characterized mm‐wave high electron mobility transistors (HEMTs) on pseudomorphic heterostructure GaAs/InGaAs samples. The T‐ and Γ‐shaped gates were produced using electroplating and a conventional single resist‐layer lift‐off process. High frequency measurements of the same device before and after plating demonstrate the reduction in gate resistance. Direct current and high frequency properties of the HEMTs depend strongly on gate length and gate recess depth. Characterization of parallel conducting layers, low field mobility, and sheet carrier concentration depth profiles were obtained with gated Hall measurements. Best HEMT performance was obtained at a gate length of 60 nm, giving an extrinsic (intrinsic) transconductance of 620 mS/mm (840 mS/mm) and a cutoff frequencyftof 135 GHz.

ISSN:1071-1023    

DOI:10.1116/1.585657

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The feasibility of high‐temperature superconductors for applications in particle optics is discussed. Although highTcsuperconducting coils and wire are not available yet, we conclude that thin films are very promising for ironless magnetic lenses due to their high maximum current density and because they can be very accurately patterned. However, a stack of 10–100 layers will be needed to fulfil the field strength and rotational symmetry requirements. Initial experimental results obtained with a superconducting YBa2Cu3O7−xfilm patterned with a 50‐turn spiral‐shaped coil are presented. The maximum critical current density obtained in the 50‐turn spiral was 104A/cm2at 30 K. The best way to stack the films would be a multilayer fabrication process, but this is not yet available. As an intermediate step, we developed a pattern suitable for face‐to‐face stacking and we propose an alignment technique based on capacitive position sensors.

ISSN:1071-1023    

DOI:10.1116/1.585658

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Low resistance T‐shaped gates as small as 60 nm have been fabricated using high resolution electron‐beam lithography (EBL). A silicon nitride (SiNx) passivation layer has been used to define the bottom of the T gate and to provide mechanical support for the top of the T gate. A two‐step etch was performed to define the gate footprint in the SiNx. First a short wet etch is used to isotropically etch the SiNxto provide a wider top opening following by reactive ion etching (RIE) to transfer the narrow resist pattern anisotropically into the bottom of the SiNx. A bilayer resist lift‐off process is then used to determine the top of the T gate and the thickness of the gate metal. End‐to‐end gate resistances of 450 Ω/mm have been measured for sub‐0.1‐μm‐long gates with a 0.5‐μm‐wide top and with 250‐nm‐thick metallization. The resistance can easily be further decreased by increasing the metal thickness and/or by widening the top of the T gate. Gate capacitancesCgsandCgdmeasured on GaAs metal–semiconductor field effect transistors (MESFETs) with a SiNxlayer showed a slight increase in capacitance compared to the devices without the SiNxlayer. Slightly higher extrinsic transconductancesgmand unity current‐gain cut‐off frequenciesfTwere achieved for the devices with the SiN layer. Intrinsic unity current‐gain cut‐off frequenciesfTof up to 102 GHz were measured. The fabrication of GaAs MESFETs with T gates down to 60 nm is demonstrated with the SiNxpassivation layer process.

ISSN:1071-1023    

DOI:10.1116/1.585615

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A novel method for submicron patterning of highTcsuperconductor thin films is presented. Specifically, we describe the patterning of the superconductor YBa2Cu3O7−x(YBCO) on single crystal SrTiO3wafers by a selective epitaxy approach. A silicon nitride template is formed on the SrTiO3using electron beam lithography and reactive ion etching. A thin film of YBCO is then deposited on the wafer, e.g., by laser ablation. Selective epitaxy occurs during the deposition process, the YBCO film grows epitaxially on SrTiO3, while the film depositing on the nitride forms insulating clusters. Good epitaxial films and patterns have been obtained as‐deposited without the need for further annealing or other process steps. Lines as narrow as 130 nm have been fabricated which show no significant decrease inTcas compared with the original blanket film.

ISSN:1071-1023    

DOI:10.1116/1.585616

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The electrodes of surface acoustic wave (SAW) devices cannot be represented in a stencil mask as cantilevered beams because the high aspect ratio makes them unstable. Therefore a complementary exposure technique has been developed. The mask pattern is formed by segmenting the electrodes into equal length open and closed areas. The wafer is then exposed twice with an offset equal to the segment length, thus forming a continuous electrode image. This approach has two advantages: (1) the high process latitude of ion beam proximity printing (IBPP) is preserved since, in contrast to the grid‐support approach, no areas are doubly exposed; and (2) only precision translation is required to register the exposures, preserving the single level nature of SAW patterns. Linewidth is shown to change by less than ±15% for ±20% changes in exposure at a 0.25 μm nominal linewidth.

ISSN:1071-1023    

DOI:10.1116/1.585617

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A technology is reported for the fabrication of buried InGaAs/GaAs quantum wires. For the pattern transfer of the nanometer structures a sensitive high resolution negativee‐beam resist is used as a direct etch mask. The essential step of the approach is a selective wet etch process by which only the top barrier layer of a quantum well structure is removed between masked regions. Due to the high energy barrier of the etched surface quantum wells compared to the masked regions a lateral potential well is formed. Investigating the width dependence of the photoluminescence efficiency a high intensity is found, even for narrow wires and a significant shift of the emission to high energies for the smallest wires with widths of 35 nm.

ISSN:1071-1023    

DOI:10.1116/1.585618

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A new approach for large‐scale semiconductor laser fabrication is presented. In this ‘‘full‐wafer processing and testing’’ concept, the mirrors are fabricated, not by cleaving the wafer but by forming them by means of a chemically assisted ion beam etching process. This allows for on‐wafer mirror passivation and testing of the finished devices.Full‐wafertechnologychanges the traditional way of discrete device fabrication and testing to a method more akin to today’s very large‐scale integrated (VLSI) technology. Consequently, it provides similar advantages in cost and throughput. Additionally, it allows other electrical and electro‐optical device components to be monolithically integrated on the wafer. Currently, we are routinely fabricating AlGaAs/GaAs diode lasers with a single quantum well graded index separate confinement heterostructure (SQW‐GRINSCH)‐type ridge structure using full‐wafer technology. Such lasers exhibit excellent beam properties in single mode up to at least 50 mW output power. Their functional characteristics are indistinguishable from comparable lasers with cleaved facets obtained from the same wafer for comparison purposes. This result reflects the high quality of the etched mirrors. Typically, their surface roughness is less than 200 Å, with mirror reflectivities of about 30% and losses due to mirror scattering below 2%. Having functional parts on the uncleaved wafer allows automated full‐wafer testing that encompasses wafer characterization and part screening. This not only eliminates part handling, with its associated yield loss, it also permits a much expanded scope of testing in a fraction of the time previously required.

ISSN:1071-1023    

DOI:10.1116/1.585619

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have fabricated two different structures in the GaAs/AlGaAs heterojunction system to quantify the transfer characteristics of the quantum dot subjected to external, local electric fields. The first structure is a single quantum dot diode with an annular field electrode placed adjacent to the double‐barrier structure by a self‐aligned fabrication process. A second structure consists of a pair of independently contacted quantum dot diodes separated by several hundred angstroms. The fabrication processes and transport properties for both of these structures are described. We have also attempted for the first time to form quantum dots in InGaAs/AlAs system lattice matched to InP and have observed that strong conductance fluctuations not related to lateral size quantization can occur. These fluctuations arise from the formation of rotation‐induced finite superlattices.

ISSN:1071-1023    

DOI:10.1116/1.585620

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

This paper describes the implementation of anI‐line photoresist process which was used to build 0.5 and 0.4 μm GaAs metal semiconductor field effect transistor (MESFET) devices with good parametric test results. A new PE/MicrastepI‐line step and repeat system with enhanced air gauge focus, dark field alignment and laser stage exposed all of the photo levels. AZ 5214, AZ 5209, and KTI 895i resists were used for the liftoff wiring, gate metal, implant, and insulation levels, respectively. Thickness vs exposure and depth of focus curves are shown. The photo process effects upon the surface sensitive GaAs MESFET are discussed. Examination of alignment effects upon the device performance and the photochemistry interaction with the physical and electrical properties are shown. Final device results are shown with good results down to 0.4 μm.

ISSN:1071-1023    

DOI:10.1116/1.585621

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

This paper is devoted to pure Au quantum wires with a length varied between 50 nm and 1 μm. In order to obtain extremely pure metallic nanometer structures, a liftoff process is preferred. To overcome the problem of grain size limited linewidth control and edge quality, a four‐layer resist system for electron beam lithography has been developed, which enables the reproducible fabrication of mesoscopic devices with lateral dimensions down to 25 nm.I–Vcharacteristics and magnetoconductance measurements have been carried out. Especially in the case of short wires, where electron transport is in the quasiballistic regime, universal conductance fluctuations have been observed, which are visible even at temperatures above 30 K.

ISSN:1071-1023    

DOI:10.1116/1.585622

出版商:American Vacuum Society    

年代:1991

数据来源: AIP