Resistive Heater Element Based on a Conductive Line in AlN Ceramic Fabricated by Laser Processing

Abstract

The purpose of this work is to demonstrate that laser-induced conductive tracts in AlN ceramic can be applied for fabrication of an integrated resistive heating element. Nanosecond laser processing at a wavelength of 1064 nm of ceramic in vacuum is used for a formation of conductive areas. It is demonstrated that the applied laser fluence and the number of pulses influence strongly the electrical properties of the material in the irradiated zone. The resistance value of the produced tracks with a length of about 4 mm and width of about 1 mm may vary from 17 to about 2000 Ohms, depending on the processing conditions. The material in the processed zone is characterized by means of surface composition, morphology, and electric properties. It is found that the electrical conductivity of the formed structure is based on the ceramic decomposition and formation of aluminum layer. The analysis of the influence of the temperature on the electrical resistance value shows that the material's conductivity could be preserved after annealing, as in the present study it is confirmed up to 300 °C. The ability of the formed tracks to serve as a basis element of ceramic integrated resistive heater is studied by applying DC voltage. It is found that the fabricated element can be used with a high reliability to about 90 °C without special requirements for contact design and encapsulation. Operation at higher temperatures is also demonstrated as the maximal one achieved is about 150 °C at 10V. The performance of the heater is investigated and discussed as the operation range is defined. The proposed element can be a basis for a design of an integrated heater in ceramic with high stability and applications in everyday life and research.

Keywords: ceramic processing; integrated resistive heater; laser structuring.

Figure 1

Scheme of the experimental setup for measurement of the fabricated track resistance and temperature. When heater properties are studied, DC voltage is applied on the electrodes and the temperature is measured by thermocouple.

Figure 2

(a) Dependence of the resistance of the fabricated structures as a function of the laser fluence and pulse overlapping for laser processing of AlN in vacuum. The black areas represent conditions where the resistance value exceeds the maximum that can be measured with the available system. The white and black crosses indicate the conditions where the minimal and the maximal resistance values are obtained. (b) Dependence of the resistance on the laser fluence at a fixed overlapping of 6. (c) Resistance dependence on the pulse overlapping at a fixed fluence of 5.7 J/cm².

Figure 3

XRD spectrum of laser-fabricated structure on the surface of AlN ceramic after ablation at a fluence of 10.2 J/cm² and pulse overlapping of 6, in vacuum.

Figure 4

XPS spectra of the native AlN ceramic and after laser processing at a fluence of 10.2 J/cm² and pulse overlapping of 6, in vacuum: (a) wide spectrum and (b) Al2p.

Figure 5

SEM images of the surface of AlN at different processing conditions: (a) the morphology of the native ceramic; (b) the laser fluence is 10.2 J/cm² and the pulse overlapping is 6; (c) the laser fluence is 5.7 J/cm² and the pulse overlapping is 6; and (d) the laser fluence is 10.2 J/cm² and the pulse overlapping is 67. A 3D image from optical profilometer is also shown in (d).

Figure 6

Cross-section SEM image of AlN ceramic processed at a laser fluence of 10.2 J/cm² and pulse overlapping of 6. The analyzed sample was obtained by the breakage of the ceramic across the formed conductive track.

Figure 7

Dependence of the resistance of a track fabricated on AlN ceramic by laser processing at a fluence of 10.2 J/cm² and pulse overlapping of 6 on the temperature for two cycles of heating and cooling. The statistics is based on measurement of three samples.

Figure 8

SEM images of the surface of a track fabricated in AlN at a fluence of 10.2 J/cm² and pulse overlapping of 6: (a) before and (b) after annealing at 300 °C.

Figure 9

Dependences of the temperature as a function of time for different DC voltages applied to track formed in AlN ceramic at a laser fluence of 10.2 J/cm² and pulse overlapping of 6.

Figure 10

SEM images of areas from a conductive track located approximately in the middle of track (a) and in the zone of contact between one of the electrodes and track (b). The sample is prepared by laser processing at a laser fluence of 10.2 J/cm² and pulse overlapping of 6; then it is annealed to 300 °C following the procedure described in Figure 7, and used as a heater applying 10 V for 2 h.