An ultrafast laser (λ=1030 nm, ~160 fs) was used to synthesize nanodiamonds directly from ethanol liquid (sans target) through the process of laser filamentation. The laser parameters (such as energy, repetition rate, irradiation time) for nanodiamond synthesis were optimized and characterized with their UV-VIS absorbance, optical emission spectra, Raman, and TEM (transmission electron microscopy) analysis. TEM analysis showed the synthesized nanodiamonds were 2-5 nm size with little or no aggregation and had visible lattice fringes of 2.07 Å corresponding to diamond (111). Methods of doping the nanodiamonds with nitrogen or other species during laser synthesis will also be presented.
Recently, ternary perovskite oxides have attracted great attention as alternative transparent conducting oxides (TCOs) because their structures are compatible with many other perovskite oxides that allow devices to be fabricated comprised entirely of perovskite oxides. Among these perovskite oxides, BaSnO3 has attracted considerable attention as a promising TCO because of its high mobility at room temperature (~320 cm2V-1s-1 in bulk single crystals and ~100 cm2V-1s-1 in epitaxial thin films) and high temperature stability in oxygen atmospheres compared to other TCOs, such as In2O3, ZnO, and SnO2. The electrical and optical properties of the BaSnO3 can be improved by either inducing oxygen vacancies or cationic doping. We have grown epitaxial La-doped BaSnO3 (LBSO) thin films on MgO (001) substrates by pulsed laser deposition using a La0.04Ba0.96SnO3 target, and investigated their structural, electrical, and optical properties as a function of the oxygen pressure during deposition. The permittivity of the LBSO films can be modified as a function of the oxygen pressure during deposition allowing tuning of their epsilon-near-zero (ENZ) wavelength from 2.2 μm to 7 μm. We will present details of the deposition conditions on the properties of LBSO films and the ability to tune the permittivity in this infrared range.
Plasmonic materials have attracted great attention due to their ability to enhance light-matter interactions. Noble metals such as Au and Ag have been well studied as materials for plasmonic devices. However, these metals are not suitable for mid infrared (IR) plasmonic applications due to their relatively large optical losses, which are detrimental to device efficiency. Metal oxides, on the other hand, have been proposed for low loss metallic components in the mid IR because they can provide a tunable carrier density by varying the concentration of dopants or defects (oxygen vacancies). The epsilon-near zero wavelength of the real part of the dielectric permittivity of these metal oxides, for example, can easily be tuned from 1.5 μm to 4 μm by adjusting doping or defect levels. Optical losses in devices made from these metal oxide materials generally exhibit lower losses than those obtained with conventional metals. We have investigated laser processing techniques for synthesizing several types of metal oxides such as indium tin oxide and phase change materials such as VO2. First, pulsed laser deposition was used to grow these oxide thin films. Second, an ultrafast laser was used to spatially pattern the thin films via a direct laser interference patterning (DLIP) configuration while simultaneously producing laser induced periodic surface structures (LIPSS) resulting in a uniaxial surface morphology. We will present details of the laser processing conditions on surface morphology, electrical, and optical properties of these laser processed metal oxide films.
The formation of laser-induced oxide layers on titanium surfaces has been widely investigated for coloring and marking applications. Complex titanium-based oxides exhibiting multiple phases can be achieved through laser patterning. Laser processing offers several advantages in that discrete areas can be modified leading to patterns with differing optical and electronic properties. To date, most research has focused on the formation and thickness control of TiO2, a wide bandgap semiconductor (~ 3.2 eV), as a means to control coloration. However, for many applications, including photodetectors and photocatalysts, a semiconductor oxide with a narrow bandgap (< 1 eV) is preferred to allow for strong absorption into the mid-IR. Other oxides and sub-oxides such as Ti2O3 have been identified as a byproduct of laser surface processing. In addition to its narrow bandgap, bulk Ti2O3 offers the unique property of having a semiconductor-metal transition at around 150 – 200°C where resistivity switches over an order of magnitude. Because of these properties, we investigate the optimization of laser processing conditions using picosecond and femtosecond laser irradiation to form Ti2O3. The effect of laser fluence, scan speed, pulse frequency, and sample chamber pressure will be discussed. Additionally, Ti2O3 thin films were grown via pulsed laser deposition to study structural phase purity, where the effect of growth temperature on optical and electrical properties is explored.
The use of laser induced forward transfer (LIFT) techniques for printing materials for sensor and electronics applications is growing as additive manufacturing expands into the fabrication of functional structures. LIFT is capable of achieving high speed/throughput, high-resolution patterns of a wide range of materials over many types of substrates for applications in flexible-hybrid electronics. In many LIFT applications, the use of a sacrificial or laser-absorbing donor layer is required despite the fact that it can only be used once. This is because the various types of release layers commonly in use with LIFT are completely vaporized when illuminated with a laser pulse. A better solution would be to employ a reusable laserabsorbing layer to which the transferable ink or material is attached and then released by a laser pulse without damage to the absorbing layer, therefore allowing its repeated use in subsequent transfers. In this work, we describe the use of two types of reusable laser-absorbing layers for LIFT. One is based on an elastomeric donor layer made from poly(dimethylsiloxane) or PDMS, while the other is based on a ceramic thin film comprised of indium tin oxide (ITO). These release layers have been used at NRL to transfer a wide range of materials including fluids, nanoinks, nanowires and metal foils of varying size and thickness. We will present examples of both PDMS and ITO as donor layers for LIFT and their reusability for laser printing of distinct materials ranging from fluids to solids.
The control of light-matter interaction through the use of subwavelength structures known as metamaterials has facilitated
the ability to control electromagnetic radiation in ways not previously achievable. A plethora of passive metamaterials as
well as examples of active or tunable metamaterials have been realized in recent years. However, the development of
tunable metamaterials is still met with challenges due to lack of materials choices. To this end, materials that exhibit a
metal-insulator transition are being explored as the active element for future metamaterials because of their characteristic
abrupt change in electrical conductivity across their phase transition. The fast switching times (▵t < 100 fs) and a change
in resistivity of four orders or more make vanadium dioxide (VO2) an ideal candidate for active metamaterials. It is known
that the properties associated with thin film metal-insulator transition materials are strongly dependent on the growth
conditions. For this work, we have studied how growth conditions (such as gas partial pressure) influence the metalinsulator
transition in VO2 thin films made by pulsed laser deposition. In addition, strain engineering during the growth
process has been investigated as a method to tune the metal-insulator transition temperature. Examples of both the optical
and electrical transient dynamics facilitating the metal-insulator transition will be presented together with specific
examples of thin film metamaterial devices.
Vanadium dioxide (VO2) undergoes a metal-insulator transition (MIT) at 68°C, at which point its electrical conductivity changes by several orders of magnitude. This extremely fast transition (Δt < 100 fs) can be induced thermally, mechanically, electrically, or optically. The combination of fast switching times and response to a broad range of external stimuli make VO2 an ideal material for a variety of novel devices and sensors. While the MIT in VO2 has been exploited for a variety of microwave/terahertz applications (i.e. tunable filters and modulators), very few devices exploiting the fast switching time of VO2 have been reported. The electrical properties of thin film VO2 (conductivity, carrier concentration, switching speed, etc.) are highly dependent on growth and post-processing conditions. The optimization of these conditions is therefore critical to the design and fabrication of VO2 devices. This paper will report the effects of various pulsed laser deposition (PLD) growth conditions on the metal-insulator transition in thin film VO2. In particular, we report the effect of PLD growth conditions on the stress/strain state of the VO2 layer, and the subsequent change in electrical properties. Finally, results from fabricated VO2 devices (THz emitters and THz modulators) will be presented.
The use of laser-induced forward transfer (LIFT) techniques for the printing of functional materials has been demonstrated for numerous applications. The printing gives rise to patterns, which can be used to fabricate planar interconnects. More recently, various groups have demonstrated electrical interconnects from laser-printed 3D structures. The laser printing of these interconnects takes place through aggregation of voxels of either molten metal or of pastes containing dispersed metallic particles. However, the generated 3D structures do not posses the same metallic conductivity as a bulk metal interconnect of the same cross-section and length as those formed by wire bonding or tab welding. An alternative is to laser transfer entire 3D structures using a technique known as lase-and-place. Lase-and-place is a LIFT process whereby whole components and parts can be transferred from a donor substrate onto a desired location with one single laser pulse. This paper will describe the use of LIFT to laser print freestanding, solid metal foils or beams precisely over the contact pads of discrete devices to interconnect them into fully functional circuits. Furthermore, this paper will also show how the same laser can be used to bend or fold the bulk metal foils prior to transfer, thus forming compliant 3D structures able to provide strain relief for the circuits under flexing or during motion from thermal mismatch. These interconnect "ridges" can span wide gaps (on the order of a millimeter) and accommodate height differences of tens of microns between adjacent devices. Examples of these laser printed 3D metallic bridges and their role in the development of next generation electronics by additive manufacturing will be presented.
The progressive miniaturization of electronic devices requires an ever-increasing density of interconnects attached via solder joints. As a consequence, the overall size and spacing (or pitch) of these solder joint interconnects keeps shrinking. When the pitch between interconnects decreases below 200 μm, current technologies, such as stencil printing, find themselves reaching their resolution limit. Laser direct-write (LDW) techniques based on laser-induced forward transfer (LIFT) of functional materials offer unique advantages and capabilities for the printing of solder pastes. At NRL, we have demonstrated the successful transfer, patterning, and subsequent reflow of commercial Pb-free solder pastes using LIFT. Transfers were achieved both with the donor substrate in contact with the receiving substrate and across a 25 μm gap, such that the donor substrate does not make contact with the receiving substrate. We demonstrate the transfer of solder paste features down to 25 μm in diameter and as large as a few hundred microns, although neither represents the ultimate limit of the LIFT process in terms of spatial dimensions. Solder paste was transferred onto circular copper pads as small as 30 μm and subsequently reflowed, in order to demonstrate that the solder and flux were not adversely affected by the LIFT process.
Additive manufacturing techniques such as 3D printing are able to generate reproductions of a part in free space without the use of molds; however, the objects produced lack electrical functionality from an applications perspective. At the same time, techniques such as inkjet and laser direct-write (LDW) can be used to print electronic components and connections onto already existing objects, but are not capable of generating a full object on their own. The approach missing to date is the combination of 3D printing processes with direct-write of electronic circuits. Among the numerous direct write techniques available, LDW offers unique advantages and capabilities given its compatibility with a wide range of materials, surface chemistries and surface morphologies. The Naval Research Laboratory (NRL) has developed various LDW processes ranging from the non-phase transformative direct printing of complex suspensions or inks to lase-and-place for embedding entire semiconductor devices. These processes have been demonstrated in digital manufacturing of a wide variety of microelectronic elements ranging from circuit components such as electrical interconnects and passives to antennas, sensors, actuators and power sources. At NRL we are investigating the combination of LDW with 3D printing to demonstrate the digital fabrication of functional parts, such as 3D circuits. Merging these techniques will make possible the development of a new generation of structures capable of detecting, processing, communicating and interacting with their surroundings in ways never imagined before. This paper shows the latest results achieved at NRL in this area, describing the various approaches developed for generating 3D printed electronics with LDW.
The field of metamaterials has expanded to include more than four orders of magnitude of the electromagnetic spectrum, ranging from the microwave to the optical. While early metamaterials operated in the microwave region of the spectrum, where standard printed circuit board techniques could be applied, modern designs operating at shorter wavelengths require alternative manufacturing methods, including advanced semiconductor processes. Semiconductor manufacturing methods have proven successful for planar 2D geometries of limited scale. However, these methods are limited by material choice and the range of possible feature sizes, thus hindering the development of metamaterials due to manufacturing challenges. Furthermore, it is difficult to achieve the wide range of scales encountered in modern metamaterial designs with these methods alone. Laser direct-write processes can overcome these challenges while enabling new and exciting fabrication techniques. Laser processes such as micromachining and laser transfer are ideally suited for the development and optimization of 2D and 3D metamaterial structures. These laser processes are advantageous in that they have the ability to both transfer and remove material as well as the capacity to pattern non-traditional surfaces. This paper will present recent advances in laser processing of various types of metamaterial designs.
Laser forward transfer of arbitrary and complex configurable structures has recently been demonstrated using a spatial light modulator (SLM). The SLM allows the spatial distribution of the laser pulse, required by the laser transfer process, to be modified for each pulse. The programmable image on the SLM spatially modulates the intensity profile of the laser beam, which is then used to transfer a thin layer of material reproducing the same spatial pattern onto a substrate. The combination of laser direct write (LDW) with a SLM is unique since it enables LDW to operate not only in serial fashion like other direct write techniques but instead reach a level in parallel processing not possible with traditional digital fabrication methods. This paper describes the use of Digital Micromirror Devices or DMDs as SLMs in combination with visible (λ = 532 nm) nanosecond lasers. The parallel laser printing of arrayed structures with a single laser shot is demonstrated together with the full capabilities of SLMs for laser printing reconfigurable patterns of silver nano-inks Finally, an overview of the unique advantages and capabilities of laser forward transfer with SLMs is presented.
The opportunities presented by the use of metamaterials have been the subject of extensive discussions. However, a large fraction of the work available to date has been limited to simulations and proof-of-principle demonstrations. One reason for the limited success inserting these structures into functioning systems and real-world applications is the high level of complexity involved in their fabrication. Most approaches to the realization of metamaterial structures utilize traditional lithographic processing techniques to pattern the required geometries and then rely on separate steps to assemble the final design. Obviously, composite structures with arbitrary and/or 3-D geometries present a challenge for their implementation with these approaches. Non-lithographic processes are ideally suited for the fabrication of arbitrary periodic and aperiodic structures needed to implement many of the metamaterial designs being proposed. Furthermore, non-lithographic techniques are true enablers for the development of conformal or 3-D metamaterial designs. This article will show examples of metamaterial structures developed at the Naval Research Laboratory using non-lithographic processes. These processes have been applied successfully to the fabrication of complex 2-D and 3-D structures comprising different types of materials.
We have studied the kinetics of a congruent, pixilated laser forward transfer process known as laser decal transfer (LDT). This process allows the transfer and patterning of silver nanoparticle inks such that the transferred pixels or "voxels" maintain the shape of the laser illumination. This process is capable of creating freestanding and bridging structures with near thin-film like properties.
Digital microfabrication processes are non-lithographic techniques ideally capable of directly generating patterns and
structures of functional materials for the rapid prototyping of electronic, optical and sensor devices. Laser Direct-Write
is an example of digital microfabrication that offers unique advantages and capabilities. A key advantage of laser directwrite
techniques is their compatibility with a wide range of materials, surface chemistries and surface morphologies.
These processes have been demonstrated in the fabrication of a wide variety of microelectronic elements such as
interconnects, passives, antennas, sensors, power sources and embedded circuits. Recently, a novel laser direct-write
technique able to digitally microfabricate thin film-like structures has been developed at the Naval Research Laboratory.
This technique, known as Laser Decal Transfer, is capable of generating patterns with excellent lateral resolution and
thickness uniformity using high viscosity metallic nano-inks. The high degree of control in size and shape achievable has
been applied to the digital microfabrication of 3-dimensional stacked assemblies, MEMS-like structures and freestanding
interconnects. Overall, laser forward transfer is perhaps the most flexible digital microfabrication process
available in terms of materials versatility, substrate compatibility and range of speed, scale and resolution. This paper
will describe the unique advantages and capabilities of laser decal transfer, discuss its applications and explore its role in
the future of digital microfabrication.
We describe a novel technique, called laser decal transfer, for the laser forward transfer of electronic inks that allows the
non-contact direct writing of thin film-like patterns and structures on glass and plastic substrates. This technique allows
the direct printing of materials such as metallic nano-inks from a donor substrate to the receiving substrate while
maintaining the size and shape of the area illuminated by the laser transfer pulse. That is, the area of the donor substrate
or ribbon exposed to the laser pulse releases an identical area of nano-ink material which retains its shape while it
travels across the gap between the ribbon and the receiving substrate forming a deposited pattern of the same
dimensions. As a result, this technique does not exhibit the limited resolution, non-uniform thickness, irregular edge
features and surrounding debris associated with earlier laser forward transfer techniques. Continuous and uniform
metallic lines typically 5 micrometers or less in width, and a few hundred nanometers in thickness were fabricated by
laser decal transfer. These lines are of similar scale as patterns generated by lithographic techniques. Once transferred,
the lines are laser-cured in-situ using a CW laser beam, becoming electrically conductive with resistivities as low as 3.4
μΩ cm. This novel laser direct-write technique is a significant improvement in terms of quality and fidelity for directwrite
processes and offers great promise for electronic applications such as in the development, customization,
modification, and/or repair of microelectronic circuits.
The use of direct-write techniques might revolutionize the way microelectronic devices such as interconnects, passives,
IC's, antennas, sensors and power sources are designed and fabricated. The Naval Research Laboratory has developed a
laser-based microfabrication process for direct-writing the materials and components required for the assembly and
interconnection of the above devices. This laser direct-write (LDW) technique is capable of operating in subtractive,
additive, and transfer mode. In subtractive mode, the system operates as a laser micromachining workstation capable of
achieving precise depth and surface roughness control. In additive mode, the system utilizes a laser-forward transfer
process for the deposition of metals, oxides, polymers and composites under ambient conditions onto virtually any type
of surface, thus functioning as a laser printer for patterns of electronic materials. Furthermore, in transfer mode, the
system is capable of transferring individual devices, such as semiconductor bare die or surface mount devices, inside a
trench or recess in a substrate, thus performing the same function of the pick-and-place machines used in circuit board
manufacture. The use of this technique is ideally suited for the rapid prototyping of embedded microelectronic
components and systems while allowing the overall circuit design and layout to be easily modified or adapted to any
specific application or form factor. This paper describes the laser direct-write process as applied to the forward transfer
of microelectronic devices.
Laser-based direct-write (LDW) processes offer unique advantages for the transfer of unpackaged semiconductor bare die for microelectronics assembly applications. Using LDW it is possible to release individual devices from a carrier substrate and transfer them inside a pocket or recess in a receiving substrate using a single UV laser pulse, thus per-forming the same function as pick-and-place machines currently employed in microelectronics assembly. However, conventional pick-and-place systems have difficulty handling small (< 1mm2) and thin (< 100 μm) components. At the Naval Research Laboratory, we have demonstrated the laser release and transfer of intact 1 mm2 wafers with thicknesses down to 10 microns and with high placement accuracy using LDW techniques. Furthermore, given the gentle nature of the laser forward transfer process it is possible to transfer semiconductor bare die of sizes ranging from 0.5 to 10 mm2 without causing any damage to their circuits. Once the devices have been transferred, the same LDW system can then be used to print the metal patterns required to interconnect each device. The implementation of this technique is ideally suited for the assembly of microelectronic components and systems while allowing the overall circuit design and layout to be easily modified or adapted to any specific application or form factor including 3-D architectures. This paper describes how the LDW process can be used as an effective laser die transfer tool and will present analysis of the laser-driven release process as applied to various types of silicon bare dies.
The development of embedded surface mount devices, IC's, interconnects and power source elements offers the ability to achieve levels of miniaturization beyond the capabilities of current manufacturing techniques. By burying or embedding the whole circuit under the surface, significant reduction in weight and volume can be achieved for a given circuit board design. In addition, embedded structures allow for improved electrical performance and enhanced function integration within traditional circuit board substrates. Laser-based direct-write (LDW) techniques offer an alternative for the fabrication of such embedded structures at a fraction of the cost and in less time that it would take to develop system-on-chip designs such as ASIC’s. Laser micromachining has been used in the past to machine vias and trenches on circuit board substrates with great precision, while laser forward transfer has been used to deposit patterns and multilayers of various electronic materials. At NRL, we have been exploring the use of these LDW techniques to both machine and deposit the various materials required to embed and connect individual components inside a given surface. This paper describes the materials and processes being developed for the fabrication of embedded microelectronic circuit structures using direct-write techniques alongside with an example of a totally embedded circuit demonstrated to date.
Significant reduction in weight and volume for a given circuit design can be obtained by embedding the required surface mount devices, bare die and power source elements into the circuit board. In addition, embedded structures allow for improved electrical performance and enhanced function integration within traditional circuit board substrates and non-traditional surfaces such as the external case. Laser-based direct-write techniques can be used for developing such embedded structures at a fraction of the cost and in less time that it would take to develop system-on-chip alternatives such as ASIC's. Laser micromachining has been used in the past to machine vias and trenches on circuit board substrates with great precision, while laser forward transfer has been used to deposit patterns and multilayers of various electronic materials. This paper describes recent work performed at the Naval Research Laboratory using the above laser direct-write techniques to machine the surface and deposit the materials required to embed, connect and encapsulate individual electronic components and microbatteries inside a plastic substrate.
Laser processing techniques, such as laser direct-write (LDW) and laser sintering, have been used to deposit mesoporous nanocrystalline TiO2 (nc-TiO2) films for use in dye-sensitized solar cells. LDW enables the fabrication of conformal structures containing metals, ceramics, polymers and composites on rigid and flexible substrates without the use of masks or additional patterning techniques. The transferred material maintains a porous, high surface area structure that is ideally suited for dye-sensitized solar cells. In this experiment, a pulsed UV laser (355nm) is used to forward transfer a paste of commercial TiO2 nanopowder (P25) onto transparent conducting electrodes on flexible polyethyleneterephthalate (PET) and rigid glass substrates. For the cells based on flexible PET substrates, the transferred TiO2 layers were sintered using an in-situ laser to improve electron paths without damaging PET substrates. In this paper, we demonstrate the use of laser processing techniques to produce nc-TiO2 films (~10 μm thickness) on glass for use in dye-sensitized solar cells (Voc = 690 mV, Jsc = 8.7 mA/cm2, ff = 0.67, η = 4.0 % at 100 mW/cm2).
This work was supported by the Office of Naval Research.
The Global Positioning System (GPS) has become a mature technology and is continually being applied in new and more demanding applications. A current effort in this area is the development of compact, durable but lightweight GPS antennas on conformal surfaces for handheld devices. Because modeling the electromagnetic performance of these antennas is often difficult, prototypes are typically built, measured and redesigned in an iterative process. We demonstrate the fabrication of a GPS conformal antenna under ambient-temperature conditions using a combination of laser micromachining and/or laser direct-write processes. The electromagnetic behavior of the antennas is then characterized and the design of the antenna structures is further optimized. Pattern simulations and input impedance measurements of the antenna are presented that demonstrate the usefulness and success of the iterative process made possible with this fabrication technique
The use of direct-write techniques in the design and manufacture of interconnects and antennas offers some unique advantages for the development of next generation commercial and defense microelectronic systems. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype interconnects and various antenna designs. This laser direct-write process is compatible with a broad class of materials such as metals and electronic ceramics and its capable of depositing patterns of any of these materials over non-planar surfaces in a conformal manner. The laser direct-write process is computer controlled so as to allow any given design to be easily modified and adapted to a particular application. To illustrate the potential of this technique, examples of metal lines on laser micromachined polyimide substrates for interconnect applications, are discussed and evaluated. In addition, examples of simple planar and conformal antennas are provided to demonstrate how this technique can influence current and future microelectronic device applications.
The use of direct-write techniques in the design and manufacture of sensor devices provides a flexible approach for next generation commercial and defense sensor applications. Using a laser forward transfer technique, we have demonstrated the ability to rapidly prototype temperature, biological and chemical sensor devices. This process, known as matrix assissted pulsed laser evaporation direct-write or MAPLE-DW is compatible with a broad class of materials ranging form metals and electronic ceramics to chemoselective polymers and biomaterials. Various types of miniature sensor designs have been fabricated incorporating different materials such as metals, polymers, biomaterials or composites as multilayers or discrete structures on a single substrate. The MAPLE-DW process is computer controlled which allows the sensor design to be easily modified and adapted to any specific application. To illustrate the potential of this technique, a functional chemical sensor system is demonstrated by fabricating all the passive and sensor components by MAPLE-DW on a polyimide substrate. Additional devices fabricated by MAPLE DW including biosensors and temperature sensors and their performance are shown to illustrate the breadth of MAPLE DW and how this technique may influence current and future sensor applications.
This paper outlines investigations into a potentially revolutionary approach to tissue engineering. Tissue is a complex 3D structure that contains many different biomaterials such as cells, proteins, and extracellular matrix molecules that are ordered in a very precise way to serve specific functions. In order to replicate such complex structure, it is necessary to have a tool that could deposit all these materials in an accurate and controlled fashion. Most methods to fabricate living 3D structures involve techniques to engineer biocompatible scaffolding, which is then seeded with living cells to form tissue. This scaffolding gives the tissue needed support, but the resulting tissue inherently has no microscopic cellular structure because cells are injected into the scaffolding where they adhere ta random. Wee have developed a novel technique that actually engineers tissue, not scaffolding, that includes the mesoscopic cellular structure inherent in natural tissues. This approach uses a laser-based rapid prototyping system known as matrix assisted pulsed laser evaporation direct write to construct living tissue cell-by- cell. This manuscript details our efforts to rapidly and reproducibly fabricate comlpex 2D and 3D tissue structures with MAPLE-DW by placing different cells and biomaterials accurately and adherently on the mesoscopic scale.
A novel laser-based direct-write technique, called Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE-DW), has been developed for the rapid prototyping of electronic devices. MAPLE-DW is a maskless deposition process operating under ambient conditions which allows for the rapid fabrication of complex patterns of electronic materials. The technique utilizes a laser transparent substrate with one side coated with a matrix of the materials of interest mixed with an organic vehicle. The laser is focused through the transparent substrate onto the matrix coating which aids in transferring the materials of interest to an acceptor substrate placed parallel to the matrix surface. With MAPLE-DW, diverse materials including metals, dielectrics, ferroelectrics, ferrites and polymers have been transferred onto various acceptor substrates. The capability for laser-modifying the surface of the acceptor substance and laser-post-processing the transferred material has been demonstrated as well. This simple yet powerful technique has been used to fabricate passive thin film electronic components such as resistors, capacitors and metal lines with good functional properties. An overview of these key results along with a discussion of their materials and properties characterization will be presented.
MAPLE direct write is anew laser-based direct write technique which combines the basic approach employed in laser induced forward transfer with the unique advantages of matrix assisted pulsed laser evaporation. The technique utilizes a laser transparent donor substrate with one side coated with a matrix consisting of the electronic material to be transferred mixed with an organic binder or vehicle. As with LIFT, the laser is focused through the transparent substrate onto the matrix coating. When a laser pulse strikes the coating, the matrix is transferred to an acceptor substrate placed parallel to the donor surface. Ex situ thermal or laser treatments can be used to decompose the matrix and anneal the transferred material, thus forming structures with the desired electronic properties. MAPLE DW is a maskless deposition process designed to operate in air and at room temperature that allows for the generation of complex patterns with micron scale linewidths. The various structures produced by MAPLE DW were characterized using 3D surface profilometry, scanning electron microscopy and optical microscopy. The electrical resistivity of the silver metal lines made by MAPLE DW was measured using an impedance analyzer. Patterns with Zn2SiO4:Mn powders were fabricated over the surface of a dragon fly wing without damaging it. An overview of the key elements of the MAPLE DW process including our current understanding of the material transfer mechanisms and its potential as a rapid prototyping technique will be discussed.
A novel approach for maskless deposition of numerous materials has been developed at the Naval Research Laboratory. This technique evolved from the combination of laser induced forward transfer and Matrix Assisted Pulsed Laser Evaporation (MAPLE), and utilizes a computer controlled laser micromachining system. The resulting process is called MAPLE-DW for MAPLE Direct Write. MAPLE-DW can be used for the rapid fabrication of circuits and their components without the use of masks. Using MAPLE-DW, a wide variety of materials have been transferred over different types of substrates such as glass, alumina, plastics, and various types of circuit boards. Materials such as metals, dielectrics, ferrites, polymers and composites have been successfully deposited without any loss in functionality. Using a computer controlled stage, the above mentioned materials were deposited at room temperature over various substrates independent of their stage, the above mentioned materials were deposited at room temperature over various substrates independent of their surface morphology, with sub-10micrometers resolution. In addition, multilayer structures comprising of different types of materials were demonstrated by this technique. These multilayer structures from the basis of prototype thin film electronics devices such as resistors, capacitors, cross-over lines, inductors, etc. An overview of the result obtained using MAPLE-DW as well as examples of several devices made using this technique is presented.
The effect of spin-polarized injection on the superconductivity order parameter is investigated in a device consisting of YBa2Cu3O7-(delta )/Au/Ni0.8Fe0.2 layers. A non-equilibrium theory which qualitatively agrees with the results of measurements made on superconductor/insulator/ferromagnet structures is presented. A quantitative analysis shows that this theory predicts injection currents that are several orders of magnitude too large. Recent results suggest that superconductivity in thin films can be strongly influenced by the injection of a spin- polarized current from a ferromagnetic material. The effect has been found to occur in both low Tc (Sn) and high Tc (YBa2Cu3O7-(delta )) superconductors when either a conventional ferromagnetic metal, permalloy (Ni0.8Fe0.2), or a colossal magnetoresistive material were used as the source of spin polarization. Control experiments showed that unpolarized current from a nonmagnetic metal had comparatively little effect on the same superconductors. A phenomenological model, in which the energy gap of the superconductor is perturbed by the presence of excess spin polarized electrons, has been shown to qualitatively mimic the experimental results. However, an estimate of the current needed to significantly suppress the gap is shown to be several orders of magnitude larger than is observed.
Pulsed laser deposition has been used for the growth of high quality YBa2Cu3O7 and La0.67Sr0.33MnO3 thin films and multilayers for electronic device applications. In particular, YBa2Cu3O7 - (SrTiO3, CeO2) - La0.67Sr0.33MnO3 trilayer devices were fabricated to study the supercurrent suppression by the injection of a spin-polarized quasiparticle current. Our results show that the critical current for a YBa2Cu3O7 - 50 angstroms SrTiO3 - La0.67Sr0.33MnO3 device was found to decrease from 120 mA to 15 mA, for an injection current of 60 mA of spin polarized current yielding a negative current gain of approximately 1.8. The effect of film microstructure on the critical current suppression was investigated. Defects in the SrTiO3 and CeO2 layers were found to control the device properties. Once optimized, spin injection represents a new approach to fabricating superconducting transistors which could impact electronic systems for many important next generation.
Pulsed laser deposition (PLD) has been used to deposit high quality thin films of Ni81Fe19/Au/YBa2Cu3O7- (delta ) onto (100) oriented substrates of MgO and SrTiO3 for the purpose of fabricating a novel high temperature superconducting three terminal device. The ferromagnet-normal metal-superconductor (F-N-S) structure is currently being investigated to determine the effect of the injection of a spin-polarized current on the order parameter of a high temperature superconducting thin film. High quality films with sharp interfaces, free of defects, are required in order to maximize the spin-injection effect. The surface morphology and transport properties of the YBa2Cu3O7-(delta ) films have been investigated using scanning electron microscopy and ac susceptibility measurements, respectively, as a function of increasing laser fluence. Deposition at 2.0 - 2.4 J/cm2, 790 degrees Celsius and 320 m Torr O2 produces films with a sharp superconducting transition and a smooth surface. The growth of Au on YBCO under different PLD conditions has been observed by atomic force microscopy. Surface clustering of Au occurs at elevated temperatures and is attributed to increased surface mobility. The presence or absence of a background gas influences the cluster size. These results are discussed within the framework of the role of excess energy of PLD adatoms with changing laser fluence and background gas.
Pulsed laser deposition is a superior technique for the growth of high quality thin films (<EQ 1 micrometers ) of electronic ceramics and has satisfied many applications. To meet developing applications, there is a need for thick films (>= 1 micrometers ) of electronic ceramics. Two film qualities principally control the growth of thick films: the film surface morphology and film stress. The deposition parameters which affect these qualities include: film deposition rate, film-substrate lattice mismatch, film-substrate thermal coefficient of expansion mismatch, and film growth kinetics. Our results suggest that it will be difficult to fabricate thick ceramic films of suitable electronic quality by conventional physical vapor deposition techniques.
We describe the deposition of SrxBa1-xTiO3 (0.5 <EQ x <EQ 0.8) thin films by pulsed laser deposition and the issues related the their application as active microwave device components. The SrxBa1-xTiO3 thin films (approximately equals 5000 angstrom) deposited at 775-850 degree(s)C in 350 mTorr of oxygen onto (100) MgO and LaAlO3 were smooth, single phase, and epitaxial with the underlying substrate. Highly oriented Sr0.5Ba0.5TiO3 films on LaAlO3 with x- ray rocking curves of 72 arc seconds were observed. The dielectric constant of Sr0.5Ba0.5TiO3 thin films, determined from the signal in patterned transmission lines between 100 kHz and 0.1 GHz, was approximately equals 20% of that observed for the bulk and the zero field temperature dependence was broad in comparison to the sharply peaked behavior seen in bulk. The dielectric loss tangent was measured as a function of stoichiometry for SrxBa1-xTiO3 (0.2 <EQ x <EQ 0.8) thin films (3-5 micrometers ) at room temperature and at 9.2 GHz. Loss tangent values were found to be highly sensitive to the Curie temperature of the film. Loss tangent values as low as 0.1% were obtained for Sr0.8Ba0.2TiO3. The results for SrxBa1-xTiO3 thin films presented in this paper are encouraging for future applications in active microwave devices.