Aluminum nitride (AlN) ceramics has a unique characteristic, namely the ability to form conductive structures on its
surface directly by laser-induced decomposition of the base material. Various research has been carried out on obtaining
low-ohmic structures depending on process parameters such as the laser power, overlap of subsequent pulses and the
type of shielding gas (air, nitrogen and argon). This paper focuses on explaining which factors have the greatest impact
on the resistance (resistivity) value of obtained structures. In order to explain the effect of the laser fluence (below and
above the ablation threshold of aluminum nitride) on the chemical structure of the conductive layers, qualitative EDX
analyses were performed. Optimization of the process allowed obtaining a resistivity of the conductive layers at a level
of ρ = 0.64·10 -6 Ω·m, with a thickness of aluminum up to 10 μm (sheet resistance R S = 10 mΩ/Sr). This technology can be
useful in making printed circuit boards (PCB), various types of sensors as well as radio-frequency identification (RFID)
and Lab-On-a-Chip (LOC) structures. This technology can also be useful for the production of metamaterials.

Direct selective metallization of AlN ceramics induced by laser radiation

A new method for direct writing of conductor lines onto ceramic substrates is presented. This method consists of forming metal thin film composed of aluminum by sublimating aluminum nitride (AlN) ceramics in Ar gas atmosphere with a Q-switched yttrium aluminum garnet (YAG) laser. Thickness of this film was about 0.5 μm. The specific resistance was about 5×10-6Ω·m. This metal layer was also available to electroless plating as a catalyst. With nickel (Ni) electroless plating solution, the Ni conductor lines of a specific resistance about 1×10-7 Ω·m were directly band selectively formed on the aluminum layer. The bonding strength between the plated film and AlN substrate was above 9.8 MPa (1 kgf/mm2).

Direct formation of conductor films by laser sublimating of ceramics.

In this paper an alternative method of manufacturing SRR structures through the selective removal of a thin layer of silver-palladium deposited on the surface of the Al 2 O 3 ceramic by laser ablation process using nanosecond Nd:YAG laser (1064 nm) was presented. The SRR structures array were subject to transmittance measurements using the TDS (Time Domain Spectroscopy). Both electric and magnetic resonances were observed at frequencies determined by the structural parameters of the SRR. In case of the E field perpendicular to an SRR structure and one resonance area for 0.56 THz with the E field parallel to the structure, two characteristic resonant dips for 0.31 THz and 0.62 THz were obtained. Studies have confirmed that using selective laser removal process enables the preparation of the resonant structure in the range of THz.

Split-ring resonators manufactured on conductive layer by selective laser ablation

In this paper a method for producing resonant structures using laser micromachining is presented. In the spot of laser
beam impact on AlN ceramics surface a conductive aluminum layer is formed. Compilation of process parameters allows
for the fabrication of structures with resistance at Rs ~ 0.01Ω/Rs. It has been also found out that the maximum value of resistance for which spiral resonator structures manifest their unique properties is at the level of Rs = 1.43 Ω.
Furthermore, the occurrence of mutual capacity which value is dependent on the arrangement of individual SR structures
with respect to each other was observed and examined. Based on satisfactory results for SR structures, it has been
attempted to produce a resonant structures dedicated to the THz range based on the process of direct metallization of
AlN ceramics surface. As a result, the Split Ring Resonator structure whose properties were verified by using the
THz -TDS method was manufactured. In case of the field E perpendicular to SRR structure and one resonance area for
0.50 THz with field E parallel to the structure, two characteristic resonant dips for 0.22 THz and 0.46 THz were
obtained. The studies confirmed that the method of direct metallization of AlN ceramics allows to produce resonant
structures in the THz range.

Resonator structures on AlN ceramics surface treated by laser radiation

The objective of this paper was to present an alternative technique of manufacturing the unit cells of spiral-shaped resonators (SR) on the aluminium nitride (AlN) ceramics. In this technique the AlN plane surface is irradiated by the Yb:glass medium-power laser (1.06 µm). As a result of the irradiation by a focused laser beam (a laser beam power up to 20 W), the rupture of the aluminium and nitrogen physical bonds occurs. Under such circumstances the conductive aluminium “paths” are formed on the originally insulating ceramic surface. Upon obtaining low ohmic conductive paths, this method makes for the feasible manufacturing of metamaterial structures. In carried out studies, the usage of such structures to suppress the coupling between pairs of patch antennas has been examined. The improvement of the mutual coupling at the level of 10 dB has been obtained. One of the advantages of the demonstrated method is a possibility to perform the selective and direct metallization of the AlN ceramics surface without using any mask as opposed to photolithography. It greatly reduces the implementation time of the projected metamaterial structures.

P. Kabacik

Papers

Spiral resonator manufactured on AlN ceramics to filter the coupled wave between patch antennas