Raymond C. Y. Auyeung

Laser transfer of biomaterials: Matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE Direct Write

Two techniques for transferring biomaterial using a pulsed laser beam were developed: matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE direct write (MDW). MAPLE is a large-area vacuum based technique suitable for coatings, i.e., antibiofouling, and MDW is a localized deposition technique capable of fast prototyping of devices, i.e., protein or tissue arrays. Both techniques have demonstrated the capability of transferring large (mol wt>100 kDa) molecules in different forms, e.g., liquid and gel, and preserving their functions. They can deposit patterned films with spatial accuracy and resolution of tens of μm and layering on a variety of substrate materials and geometries. MDW can dispense volumes less than 100 pl, transfer solid tissues, fabricate a complete device, and is computed aided design/computer aided manufacturing compatible. They are noncontact techniques and can be integrated with other sterile processes. These attributes are substantiated by films and arrays of biomaterials, e.g., polymers, enzymes, proteins, eucaryotic cells, and tissue, and a dopamine sensor. These examples, the instrumentation, basic mechanisms, a comparison with other techniques, and future developments are discussed.

New approach to laser direct writing active and passive mesoscopic circuit elements

We have combined some of the major positive advantages of laser-induced forward transfer (LIFT) and matrix-assisted pulsed laser evaporation (MAPLE), to produce a novel excimer laser driven direct writing technique which has demonstrated the deposition in air and at room temperature and with sub-10 μm resolution of active and passive prototype circuit elements on planar and nonplanar substrates. We have termed this technique MAPLE DW (matrix-assisted pulsed laser evaporation direct write) and present its historical evolution from pulsed laser deposition. This paper describes the simplistic approach to carry out MAPLE DW, gives experimental conditions, and physical characterization results for the deposition of NiCr thin film resistors, Au conducting lines, and multilayer depositions of Au conductors and BaTiO3 dielectrics to produce prototype capacitors. In general, the electrical properties of the materials deposited (conductivity, dielectric constant, and loss tangent) are comparable or superior to those produced by other commonly used industrial processes such as screen printing. The mechanism of the MAPLE DW process, especially the novel aspects making it a powerful approach for direct writing all classes of materials (metals, oxide ceramics, polymers and composites), is also described.

Three‐Dimensional Printing of Interconnects by Laser Direct‐Write of Silver Nanopastes

Conventional interconnect technologies are facing increasing challenges as dramatic advances in features and performance are made in microelectronics systems. Wire bonding technology is the most common fi rst-level chip interconnection method used throughout the electronics industry today. As semiconductor devices continue to shrink in feature size and increase in functionality, the capability to bond smaller pads with ultra-fi ne pitch ( < 50 μ m) and reduced interconnect height ( < 60 μ m) is required for many microelectronic, optoelectronic and bioelectronic devices. [ 1–5 ] These dimensions lie below the current limits of wire bonding technology. In addition, the implementation of hybrid structures in printed electronics requires interconnect technologies compatible with dissimilar materials and fl exible plastic surfaces at low processing temperatures. [ 6 , 7 ] Therefore, alternative interconnection technologies are required to solve challenges presented by resolution advances and compatibility requirements in the development of new microelectronic structures and applications. Direct-write (DW) is a family of non-lithographic approaches that allow rapid and low-cost fabrication for printed electronics, photonic materials, sensor, micropower sources and biological applications. [ 8–15 ] Most direct-write techniques, such as inkjet printing, [ 8 ] are constrained to two-dimensional (2D) patterning. Extrusion-based direct ink writing technologies [ 16–18 ] are able to produce spanning structures, however, the cross-section geometry of the extrudates is usually invariable during the printing process and close contact with the substrate or previously deposited layers is required to assemble the new layers. To date, there have been few reports of 3D direct-write processes that combine non-contact printing and assembly, variable geometries of the building blocks during the printing and fi ne 3D resolution. Such a freeform direct-write process could provide a powerful tool for fabricating interconnects with ultra-fi ne pitch bonding capability. Many applications, such as delicate electronic devices, organic electronics and MEMS fabrication, would also benefi t from them. Here we report a novel non-contact three-dimensional printing and assembly process based on laser-induced forward transfer (LIFT) of high concentration silver nanopastes, also called laser direct-write (LDW). [ 15 ]

Time-resolved optical microscopy of a laser-based forward transfer process

Matrix-assisted pulsed laser evaporation direct write was investigated by ultrahigh speed optical microscopy. A composite barium–zirconium titanate/α-terpineol layer was irradiated by 355 nm laser pulses with a 150 ns pulse width, and it was observed that material removal does not begin until after the end of the pulse (t>200 ns) and continues for 1 μs after the irradiation. The desorption plume consists of micron-size particles moving with a velocity of ∼0.2 km/s. The slow response is attributed to the combination of particle absorbers and highly viscous fluid. The ability to form continuous, pinhole-free coatings is due to slow coalescence of the particles.

Direct writing of electronic and sensor materials using a laser transfer technique

We present a laser-based direct write technique termed matrix-assisted pulsed-laserevaporation direct write (MAPLE DW). This technique utilizes a laser transparentfused silica disc coated on one side with a composite matrix consisting of the materialto be deposited mixed with a laser absorbing polymer. Absorption of laser radiationresults in the decomposition of the polymer, which aids in transferring the solute to anacceptor substrate placed parallel to the matrix surface. Using MAPLE DW, complexpatterns consisting of metal powders, ceramic powders, and polymer composites weretransferred onto the surfaces of various types of substrates with <10 micron resolutionat room temperature and at atmospheric pressure without the use of masks.Current trends for developing advanced electronic andsensor systems place great emphasis in achieving per-formance levels generally associated with integratedcircuits. This requires further miniaturization, while en-hancing the functionality and reliability of existing sys-tems. New strategies are needed in order to eliminate thelong lead times required for the fabrication of prototypesand evaluation of new materials and designs. The use ofrapid prototyping techniques such as direct write, whichdo not need photolithographic processing, provide a so-lution to the above requirements. Direct write technolo-gies do not compete with photolithography for size andscale but rather add a complementary tool for specificapplications requiring rapid turnaround and/or patterniteration, conformal patterning, or modeling difficult cir-cuits. Examples of direct write technologies for fabricat-ing or modifying metallic interconnects and/or otherelectronic passive elements include ink jet printing,

Laser processing of polymer thin films for chemical sensor applications

Contemporary and next-generation commercial and defense-related platforms offer countless applications for thin-film polymer coatings, including the areas of microelectronics, optoelectronics, and miniature chemical and biological sensors. In many cases, the compositional and structural complexity, and the anisotropy of the material properties preclude the processing of many of these polymers by conventional physical or chemical vapor deposition methods. The Naval Research Laboratory has developed several advanced laser-based processing techniques for depositing polymer thin films for a variety of structures and devices. The two techniques detailed in this work, matrix-assisted pulsed laser evaporation (MAPLE) and MAPLE direct-write (MAPLE DW), are based on the concept of laser absorption by a matrix solution consisting of a solvent and the desired polymer. MAPLE is a physical vapor deposition process that takes place inside a vacuum chamber, while MAPLE DW is a laser forward-transfer process that is carried out under atmospheric conditions. Both processes have been successfully used in the fabrication of thin films and structures of a range of organic materials and systems. Examples of their use in the fabrication of two types of chemical sensors, together with a comparison of the performance of these laser-processed sensors and that of similar sensors made by traditional techniques are provided.

Plume and jetting regimes in a laser based forward transfer process as observed by time-resolved optical microscopy

Matrix-assisted pulsed laser evaporation direct-write was investigated by ultra high-speed optical microscopy. A layer of viscous fluid was irradiated with 355 nm, 30 ns laser pulses in a laser forward transfer configuration. The fluid response as a function of fluence was studied, and several distinct regimes of behavior were observed: plume, jetting and sub-threshold. This work emphasizes the fundamental differences between laser forward transfer of solid-state materials and rheological fluids.

Oriented barium hexaferrite thick films grown on c-plane and m-plane sapphire substrates

The magnetic and structural properties of thick pulsed laser deposited (PLD) barium hexaferrite (BaM) films grown on c-plane and m-plane sapphire substrates were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Rutherford backscattering spectroscopy (RBS), vibrating sample magnetometry (VSM), and ferrimagnetic resonance (FMR). Previously, BaM thin films (-0.5 /spl mu/m) grown on c-plane (0001) sapphire substrates exhibited magnetic properties closely approaching those of single crystal spheres. These films are potentially useful for thin film millimeter-wave devices such as circulators, isolators, and phase shifters, provided that thick films (e.g., 20 to 100 /spl mu/m) with suitable magnetic and dielectric properties can be grown. In general, it was found that an increase in film thickness leads to the growth of either textured polycrystalline BaM, which can be loosely adherent, or delamination of the films. However, well oriented thick BaM films were grown up to 15 and 20 /spl mu/m on the c-plane and m-plane sapphire substrates, respectively, before delamination occurred. The FMR linewidth, /spl Delta/H, was 200 Oe at 85 GHz for an annealed 15 /spl mu/m thick PLD BaM film on c-plane sapphire with 4/spl pi/M=4200 G, H/sub A/=16000 Oe and an XRD /spl omega/-scan of 0.51/spl deg/ FWHM about the (008) BaM plane. The FMR linewidth of PLD BaM films grown on m-plane (11_00) sapphire substrates were greater than 450 Oe with 4/spl pi/M-4000 G H/sub A/=16000 Oe. the m-plane films were magnetically well oriented in the film plane with M/sub r//M/sub s/ along the easy axis greater than 90% for all PLD m-plane BaM films. >

Laser direct writing of phosphor screens for high-definition displays

A laser-based forward transfer direct writing technique was used to deposit phosphor powder screens for high-resolution display applications. With this technique, called matrix-assisted pulsed-laser evaporation direct write, dense oxide phosphor powders of Y2O3:Eu (red) and Zn2SiO4:Mn (green) were deposited on alumina and polymer substrates. All processing was performed in air at room temperature. Cathodoluminescent measurements showed that the luminous efficiency of the phosphor powders was not degraded by the deposition process. A 6×6 red and green matrix with pixel sizes of 100 μm (250 lines per inch) with a 100 μm spot size is demonstrated; however, with smaller spot sizes this technique is easily scalable to pixel sizes 2500 lines per inch).

Direct writing of conformal mesoscopic electronic devices by MAPLE DW

Abstract We demonstrate a novel pulsed UV laser direct writing technique called MAPLE DW for the fabrication of conformal electronic devices. MAPLE DW (matrix assisted pulsed laser evaporation direct write) is a soft laser forward transfer technique that takes place in air and at room temperature. Specific experimental results for the deposition of Ag metal and BaTiO3 composite dielectrics with electrical quality comparable to conventional thick film deposition techniques will be given as well as a discussion of the relevant issues for further electronic device improvement. The mechanism of the MAPLE DW process that makes it applicable to a broad class of electronic materials and even biomaterials is also described.