H. D. Wu

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.

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,

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.

Direct writing of polymer thick film resistors using a novel laser transfer technique

Polymer thick film (PTF) resistors were fabricated using a new laser-based transfer technique called matrix-assisted pulsed laser evaporation direct write (MAPLE-DW). MAPLE-DW is a versatile direct writing technique capable of writing a wide variety of materials on virtually any substrate in air and at room temperature. Epoxy-based PTF resistors spanning four decades of sheet resistances (10 Ω/sq. to 100 kΩ/sq.) were deposited on alumina substrates under ambient conditions. Electrical characteristics of these MAPLE-DW deposited resistors were studied at a wide frequency range (1 MHz to 1.8 GHz), and the results were explained through an equivalent circuit model and impedance spectroscopy. Temperature coefficient of resistance measurements for the PTF resistors were performed between 25 and 125 °C. The results based on the percolation theory were used to explain the temperature dependence of the resistance behavior of the PTF resistors.

Direct writing of electronic materials using a new laser-assisted transfer/annealing technique

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.

Dielectric properties of oxide structures by a laser-based direct-writing method

Matrix-assisted pulsed laser evaporation direct-write (MAPLE-DW) is a laser-based method of directly writing mesoscopic patterns of electronic materials. Patterns of composite BaTiO 3 /SiO 2 /TiO 2 dielectric material were written onto Pt/Au interdigitated-electrode test structures, with precise control over final dielectric properties. Scanning electron microscopy indicates random close-packed structures of BaTiO 3 and SiO 3 particles, with interstitial spaces partially filled with titania. Depending on the BaTiO 3 :silica ratio, the dielectric constant ranged from 5 to 55 and followed a 4-component logarithmic rule of mixing. This work demonstrates that the transfer process and the final material properties of MAPLE-DW oxide materials are largely decoupled.

Laser Direct Writing of circuit elements and sensors

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.

Maple direct write: A new approach to fabricate ferroelectric thin film devices in air at room temperature

Abstract MAPLE Direct Write or MAPLE DW is a new direct writing technique which combines some of the major positive advantages of laser induced forward transfer and matrix assisted pulsed laser evaporation (MAPLE). This novel laser driven direct writing technique has demonstrated the deposition of metal, ceramic, and polymer materials in air and at room temperature and with sub-10 micron resolution for active and passive prototype circuit elements on planar and nonplanar substrates. Here, we have used MAPLE DW to synthesize ferroelectric devices for tunable microwave device applications. For ferroelectrics and the other functional materials, MAPLE DW can be used to investigate directly the properties of powder materials as a function of grain size, doping, and processing technique. The best properties obtained for Ba0.5Sr0.5TiO3 and BaTiO3 films were dielectric constants of 40, with loss tangents of about 0.025 with ∽ 1% tuning.

Matrix Assisted Pulsed Laser Evaporation Direct Write (MAPLE DW): A New Method to Rapidly Prototype Active and Passive Electronic Circuit Elements

We demonstrate a novel laser-based approach to perform rapid prototyping of active and passive circuit elements called MAPLE DW. This technique is similar in its implementation to laser induced forward transfer (LIFT), but different in terms of the fundamental transfer mechanism and materials used. In MAPLE DW, a focused pulsed laser beam interacts with a composite material on a laser transparent support transferring the composite material to the acceptor substrate. This process enables the formation of adherent and uniform coatings at room temperature and atmospheric pressure with minimal post-deposition modification required, i.e., ≤400°C thermal processing. The firing of the laser and the work piece (substrate) motion is computer automated and synchronized using software designs from an electromagnetic modeling program validating that this technique is fully CAD/CAM compatible. The final properties of the deposited materials depend on the deposition conditions and the materials used, but when optimized, the properties are competitive with other thick film techniques such as screen-printing. Specific electrical results for conductors are 3 /TiO 2 composite capacitors the k can be tuned between 4 and 100 and losses are

Matrix-assisted laser transfer of electronic materials for direct-write applications

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.