Patternable Joule Heat Film With Ultrafast Heating, High-Temperature, and Oxidation-Resistant Surface

The pursuit of increasingly efficient and versatile Joule heat sources that were directly heated by electrical current has consistently driven technological advancements for centuries [1,2]. The 19th century witnessed a pivotal moment with the invention of incandescent lamps. These lamps utilized filaments, initially constructed from platinum and later from the higher-melting-point tungsten, to achieve remarkable operating temperatures [3,4]. A crucial vacuum environment was created by the glass bulbs, effectively mitigating the detrimental effects of high-temperature oxidation of the filament. It paved the way for the development of Joule heating filaments acting as cathodes that emit electrons when heated. This technology played a crucial role in the widespread adoption of vacuum tubes, cathode ray tubes, and numerous other 20th-century breakthroughs [5].

In recent years, Joule heating has experienced a resurgence in material processing techniques, particularly in applications such as ultrafast sintering. The Joule heating method uses a pulsed current to heat a conductive substrate (usually a carbon substrate) with appropriate resistance rapidly to thousands of Kelvin by flowing current and electron scattering, thus heating the precursor of the target material. Using this method, researchers can create structures such as nanoparticles, nanowires, single atoms, high-entropy alloys, thin films, and bulk ceramics [6–14]. However, a significant limitation persists—the requirement for a vacuum environment or inert gas atmosphere to prevent filament oxidation in air or harsh environments [5,15–18]. This constraint severely restricts the potential applications of Joule heating technology. Existing solutions, such as oxidation-resistant heating wires employed in high-temperature furnaces, present a tradeoff: exceedingly slow heating rates. For example, the thermal shock resistance of MoSi₂ ceramic components is poor. When subjected to large temperature gradients, it is easy to generate and propagate cracks, so the heating rate generally does not exceed 10 °C/min [19,20]. In high-temperature environments, the ferrite grains of iron-chromium-aluminum alloys grow rapidly, causing the alloy to rapidly embrittle and unable to withstand the large surface loads required for rapid heating. Therefore, the heating rate is usually slow. Rapid heating applied by electric current in these elements can produce severe thermal shock with high temperature gradient and induce detrimental effects like surface anti-oxidation layer peeling due to thermal ablation and thermal expansion. Consequently, achieving both ultrafast heating and functional heating surfaces in air or corrosive environments remains a significant challenge [21–24].

Recently, Joule heat sources based on graphene filaments have been encapsulated by protective layers, such as boron nitride, Al₂O_3, and vacuum chamber, can withstand high temperatures up to 1300 K [19,25]. These graphene devices demonstrate fascinating functions in broadband light sources and ultrafast thermal light phase modulators. Additionally, the need for near-field infrared light sources and heat sources capable of enduring extreme environments presents exciting prospects for various applications. However, there is still a lack of experimental verification of scaled applications due to the difficulty in providing high-quality and uniform encapsulation layers in large scale. There exists a critical need for large-scale solutions offering exceptional resistance to ultrahigh temperature oxidation and thermal shock.

Here, we manufactured tungsten metal and molten quartz on a quartz substrate, achieving a patternable joule heat film (PJHF) with ultrafast heating, high-temperature and oxidation-resistant surface, paving the way for technological exploration in the field of electrical heating and lighting.

Figure 1(a) shows the preparation process of the sample, where tungsten metal film of 100–200 nm was sputtered on a fused quartz substrate by extreme ultraviolet lithography and direct current magnetron sputtering. Subsequently, a 60–80-μm melted silica coating was sintered on the metal surface using a rapid sintering device. The optical image of the final sample is shown in Fig. 1(b). During the rapid sintering process, the micropores between silicon dioxide nanoparticles gradually close as the temperature increases, forming a dense structure (see Fig. S1 available in the Supplemental Materials on the ASME Digital Collection). From the scanning electron microscope (SEM) image of the sample cross section (Fig. 1(c)), there are no obvious defects such as pores or cracks in the coating, which effectively prevent tungsten from contacting oxygen in the air, providing the sample with strong oxidation resistance. As shown in Fig. 1(d), the broadband at 440 cm⁻¹ and 490 cm⁻¹ of the Raman spectrum is caused by the vibration of the six-membered ring, showing a relatively obvious characteristic of fused silica [26].

When we patterned the film, we designed a structure that is wide on both sides and narrow in the middle, creating an enhanced joule heat effect in the narrow area. Through this enhanced Joule heating effect, we can observe bright visible light emission mainly from the constriction region when the PJHF is heating, leaving other area nonilluminating. In addition, the enhanced Joule heating effect in the contracted region is affected by the temperature of the wide region. The IV curve of PJHF at different input voltage rise rates is a good reflection of this phenomenon. As shown in Fig. 2(b), the slower the input voltage rises, the lower the operating current of the device. When the voltage rises slowly, the heating time in the ramping stage is long, leading to higher temperature in wide region of PJHF. The temperature increase in the wide region of PJHF reduces the heat dissipation in the heating region, and it is possible to show higher temperature and resistance at the same input voltage [27]. When the voltage rise rate is 1 V/s, the temperature in the wide area is 30 °C–34 °C (measured by thermocouples) higher than that when the voltage rise rate is 4 V/s. When the input voltage rises at a rise rate of 1 V/s, the resistance of PJHF reaches 7.69 Ω at 10 V, which is 38% larger than when the rise rate is 4 V/s. To test the durability of the PJHF, two films heated in air at a heating temperature of 1328 °C–1284 °C and 1182 °C–1176 °C for 1 h. The results are shown in Fig. 2(c). When the initial temperature is 1328 °C, the temperature decay speed is 7.3 times that of the initial temperature of 1183 °C. As shown in Fig. 2(c), when the initial temperature is as low as 1025 °C, the working current of PJHF is basically stable. The degree of damage can be reflected by the change of resistance, and the resistance of the damaged device will increase (see Fig. S2 available in the Supplemental Materials). From the working current at constant voltage, PJHF has good heating stability in the air. For heating films, in addition to stability, the maximum heating temperature is also a very important indicator. To determine the maximum heating temperature of the film, a voltage from 26 V to 28 V was applied to the device, causing the heating area of the PJHF to rapidly reach ∼2000 °C for seconds, and subsequently cool in seconds as shown in Fig. 2(d). When the temperature reached ∼2200 °C, the intense thermal stress directly tore the tungsten metal coating and the huge energy resulted in an electric explosion. The damaged PJHF exhibits sharp cracks and a similar burnt shape, which is consistent with the characteristics of electrical explosions and thermal stress damage (see Fig. S3 available in the Supplemental Materials).

In addition to the extremely high heating temperature, we also tested the ultrafast response of the PJHF. First, a pulse with a height of 21.5 V and a width of 1 ms was applied and then the PJHF was recorded with a high-speed camera (see Movie 1 available in the Supplemental Materials). Figure 3(a) shows three frames from the captured results, with the obvious light signal during the 1 ms pulse. To further identify the ultrafast heating rate of the film at low input voltage, we collected temperatures using an infrared thermometer and tested the temperature changes when changing applied voltage levels, as shown in Fig. 3(b). When the PJHF shifted between 1240 °C and 1280 °C, the heating rate was ∼1000 °C/s, and the cooling rate was ∼1800 °C/s. At this time, the input voltage of the device is 11.2 V∼11.6 V, which also makes his heating speed significantly lower than the input voltage 21.5 V. Figure 3(c) shows the temperature variation during cyclic voltage level shifting, with the shifting process taking ∼200 ms. In addition, the fatigue strength of PJHF against thermal shock is also very good. In the experiment shown in Fig. 3(d), we made a PJHF with smaller power than before and cycled PJHF on and off at ∼1300 K through pulse voltage, observed its working state under cyclic thermal stress, and also evaluated its state through current and resistance value. After tens of thousands of thermal shocks, the PJHF is still consistent with the initial resistance, which is a good proof of its thermal shock resistance.

$hcov$is the convective heat transfer coefficient, $Acov$ is the convective area, $ε$is the material emissivity, $σ$ is the Boltzmann constant, $Arad$ is the radiation area, $ΔT$ is the temperature difference, $θ$ is the thermal resistance [28,29]. When airflow at different speeds passes over the sample surface, the higher the airflow speed, the larger the convective heat transfer coefficient, resulting in a larger value for the $Q(conv)$ and also $Q$⁠. The more heat that is lost, the lower the temperature of the PJHF, which eventually leads to lower resistance. The decrease in temperature leads to changes in resistance, which will be reflected in the current. As shown in Fig. 4(a), by monitoring the changes in the current signal, sensing of the airflow speed can be achieved [30]. See Fig. S4 available in the Supplemental Materials on the ASME Digital Collection is a schematic diagram showing the relationship between wind speed and current variation when the input voltage is 7 V. Based on the image, we believe that the detection range of this sensor is from 3 m/s to 25 m/s. The current variations caused by wind speeds below 3 m/s are erratic, and when the wind speed exceeds 25 m/s, the current variations due to different wind speeds tend to be consistent. At a wind speed of 13 m/s, the detection sensitivity is 14.1 mA/(m/s).

The response time of the incandescent light to the heating signal, transparency of antioxidant coating (see Fig. S5 available in the Supplemental Materials), and the cyclic E-heating behaviors show that the incandescence response of PJHF is not inferior to that of liquid crystal displays [31]. Furthermore, the incandescent light is bright enough to eyes (Fig. 3(a)). On the basis of these features, we proposed a new self-luminous type display by employing the incandescent PJHF as the light-emitting units. The incandescent display has been successfully fabricated mainly based on the extreme ultraviolet lithography, magnetron sputtering, and fused silica coating. Thanks to the patternability of the PJHF, we can flexibly design the shape and heating area of the PJHF, Fig. 4(b). The display is a digital display module manufactured by us. When all 7 filaments are lit, the driving voltage and current are 13 V and 26 mA, respectively, with a power of 0.338 W. The parameters of the microscope at the time the photographs were taken are shown in the Table S1 available in the Supplemental Materials.

We have developed a method for producing transparent high-temperature protective coatings for fused silica, which can protect tungsten metal from heating to above 1000 °C for extended periods in an air atmosphere. This structure also enables rapid Joule heating and facilitates simple sensing of wind speed. Leveraging the transparent nature of the coating, combined with lithography technology, we have developed display modules capable of displaying digits within a few hundred micrometers.

The experiment employed quartz glass manufactured by melting process (Aipu Optics, Lianyungang, China) as the substrate. The quartz slice was polished with degreased cotton balls until no contaminants were observed under a microscope. The polished quartz slice was then placed in a tube furnace and heated in an air atmosphere to 1000 °C for 1 h, followed by air cooling after maintaining at this temperature for 30 min. AZ5214 photoresist (Sinfeng Nanotechnology, Nanjing, China) was spin-coated onto the surface of the quartz slice at a speed of 3500 r/min and then heated at 100 °C on a hotplate for 1 min. The exposure time at 0.5 light intensity parameter using a mask aligner (Tototech, Suzhou, China) was 500 ms. After exposure, the sample was developed in ZX238 developer solution for 1 min, followed by rinsing and drying. Subsequently, a layer of approximately 150 nm thick tungsten was sputtered onto its surface using a sputtering system (Quorum, UK) with a sputtering current of 50 mA for 600 s. 250 mg of powder (Evonik Industries AG, Germany) was uniformly spread on the back of an aluminum tape and pressed onto the substrate. The sample is placed between two carbon sheets in a vacuum and rapidly heated at 60 °C/s for ∼30 s to reach the sintering temperature. This temperature ramping stage is followed by ∼10 s of isothermal sintering.

The experiment connects the sample to copper wires using silver paste. A Rigol digital power supply (Rigol Technologies, China) and a Keithley digital power supply (Keithley Instruments) apply a voltage of 10–20 V across the sample, heating the heating zone via Joule heating. The temperature of the heating zone is measured using an infrared thermometer (Fluke). A pulse signal is applied to the photothermal source using a signal generator and power amplifier to test the response speed of the sample.

The composition of the sintered coating was characterized using a Raman spectrometer (Horiba, Japan), while the surface morphology and cross section of the coating were observed using optical microscopy (Shanghai Zhaoyi Optoelectronics ZYJ-1500, China) and scanning electron microscopy (Zeiss). Optical images of the samples during operation were collected.

• Research Fund of State Key Laboratory of Mechanics and Control for Aerospace Structures (Award ID: MCMS-I-0422K01).

• The Fundamental Research Funds for the Central Universities (Award IDs: NE2023003, NC2023001, NJ2023002, and NJ2022002; Funder ID: 10.13039/501100012226).

• The Fund of Prospective Layout of Scientific Research for NUAA (Nanjing University of Aeronautics and Astronautics) (Award ID: MCMS-I-0421G01; Funder ID: 10.13039/501100004193).

There is no conflict of interest.

The datasets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.