Research on Low Energy Conversion of Tantalum Nitride Thin Film Energy Exchange Element 

        MEMS pyrotechnic devices have the characteristics of structural miniaturization, energy exchange informatization, and sequence integration, and are an important development direction for the new generation of pyrotechnic devices. As the core part of MEMS pyrotechnic devices, the microstructure energy exchange element determines the ignition performance, safety, and reliability of MEMS pyrotechnic devices, which in turn affects the combat performance of weapons and ammunition [1-3].

       The microstructure transducer is mainly made by depositing materials such as metals or semiconductors onto insulating substrates. Tantalum nitride (TaN) has excellent electrical properties, stable thermal performance, and good resistance to oxidation and corrosion. It has important applications in fields such as aerospace, microelectronics, biomedical, and power machinery [4-5]. Compared with metal materials, the resistance temperature coefficient (TCR) of TaN is negative, and the resistance decreases with the increase of temperature, which is conducive to achieving low energy of microstructure energy exchange elements. Vishay, a foreign company, has disclosed a thin film chip for electric detonators based on TaN thin film technology, with a firing energy reduced to 50 μ J; The ignition energy of TaN films prepared by Cai Xianyao et al. in China is 1-3mJ [6], while the ignition energy of TaN films prepared by Shaanxi Institute of Applied Physics and Chemistry is 0.6mJ [7]. There is a significant gap in research achievements in related fields both domestically and internationally.

        This article designs and produces TaN thin film energy exchange elements with different bridge film thicknesses, bridge area sizes, and bridge area shapes, and tests their ignition sensitivity. The influence of bridge area parameters on the ignition performance of energy exchange elements is obtained, providing basic parameters for the low-energy conversion of microstructure energy exchange elements.

1 Experimental section

1.1 Design and preparation of tantalum nitride thin film energy exchange elements

        The overall structure of the tantalum nitride thin film transducer consists of a substrate, an intermediate layer, a firing layer, and a solder pad layer, as shown in Figure 1. The function of the matrix is to support the carrier, and the matrix material is 7740 glass; The function of the intermediate layer is to increase the adhesion force between materials, and the intermediate layer material is selected as titanium or nickel chromium; The material of the ignition layer is tantalum nitride; The function of the pad layer is to improve conductivity, and copper is selected as the pad material. The exposed part between two solder pads on the ignition layer in the bridge area is shown in Figure 2.

Figure 1 Schematic diagram of the overall structure design of tantalum nitride thin film energy exchange element

               Bridge area

Figure 2 Schematic diagram of bridge area

        The tantalum nitride thin film transducer is prepared using MEMS technology, and the tantalum nitride thin film is prepared using magnetron sputtering technology. The KS60VR magnetron sputtering equipment from Italian KENO SISTEC company is selected. This article selects 99.9% tantalum nitride as the target material, with a cavity vacuum degree of 5 × 10-6Pa, sputtering power of 200W, sputtering time of 50min, Ar flow rate of 60 sccm, substrate temperature of 70 °. The preparation of transducer patterns is achieved through a series of MEMS processes such as uniform glue, lithography, development, and peeling techniques.

        The thickness of tantalum nitride thin films is controlled by adjusting the magnetron sputtering time, and the actual measurement value has very little error compared to the design value. Therefore, the thickness of tantalum nitride thin films in this article is uniformly controlled by the design value. The shape of the bridge area is prepared by photolithography technology, with a line size of 10 μ Above m, the actual measurement value has minimal error compared to the design value; Line size 10 μ Below m, the actual measured value is smaller than the design value, and the lines are prone to breakage and other phenomena. The process yield is not high, and the quantity involved in this article is only one. Therefore, the design value is uniformly used for the size of the bridge area in this article.

1.2 Spark sensitivity testing of tantalum nitride thin film energy exchange elements

        According to the sensitivity test of GJB/z 377A-94 using the Langley method, the ignition sensitivity of tantalum nitride thin film transducer with different bridge zone parameters was tested. The selected instrument has a resolution of 0.1V, and the experimental data distribution is assumed to be normal. The detonation circuit for testing is shown in Figure 3, using 33 μ F firing capacitor, the energetic material used is lead Stephenate.

Figure 3 Schematic diagram of detonation circuit

2 Results and Discussion

2.1 The influence of bridge film thickness on the ignition sensitivity of TaN thin film transducer

        Select Figure 1 (as shown in Figure 4) in the bridge area, with a bridge area size of 0.2mm × Under the condition of 0.2mm, the ignition sensitivity test was conducted on energy exchange elements with different bridge film thicknesses, and the results are shown in Table 1.

Figure 4 Schematic diagram of Figure 1 in the bridge area

Table 1 Test results of ignition sensitivity of energy exchange elements with different bridge film thicknesses

 

        Table 1 shows that when the shape and size of the bridge area are constant, the firing voltage of the transducer first decreases and then increases with the increase of the bridge film thickness. When the bridge film thickness is 0.9, the firing voltage of the transducer first decreases and then increases μ At m, the average ignition voltage is the smallest, at 6.4V.

2.2 The influence of bridge membrane size on the ignition sensitivity of TaN thin film transducer

        According to the test results in Table 1, a thickness of 0.9 was selected μ The bridge membrane of m, select Figure 1 for the bridge area, and change the size of the bridge area (H × L) Study its impact on ignition sensitivity. The ignition sensitivity test results of energy exchange elements with different bridge area sizes are shown in Table 2.

Table 2 Test results of ignition sensitivity of energy exchange elements with different bridge area sizes

         The results in Table 2 indicate that when the thickness of the bridge membrane and the shape of the bridge area are constant, the firing voltage of the transducer also decreases as the size of the bridge area decreases. When the size of the bridge area is 0.1mm, the firing voltage of the transducer also decreases continuously × At 0.1mm, the average ignition voltage is the smallest, at 6.4V.

2.3 The influence of bridge angle on the ignition sensitivity of TaN thin film transducer

        According to the test results in Tables 1-2, a thickness of 0.9 is selected μ The bridge membrane of m has a bridge area size of 0.1 mm × 0.1mm, change the angle between the shape of the bridge area and the shape of the bridge area to obtain Figure 2 of the bridge area, as shown in Figure 5.

Figure 5 Bridge area graphics with different angles 2

        Included angle θ Designed at 30 °, 45 °, and 60 °, the ignition sensitivity test was conducted on them, and the test results are shown in Table 3. The results in Table 3 indicate that, under the same thickness and bridge size, the average ignition voltage of Figure 2 in the bridge area is lower than that of Figure 1 in the bridge area; Included angle θ At 45 °, the average firing voltage of the transducer is the smallest, at 5.6V.

Table 3 Test results of ignition sensitivity of energy exchange elements with different angles

2.4The influence of bridge shape on the ignition sensitivity of TaN thin film transducer 

        Select a thickness of 0.9 μ Bridge membrane of m, bridge area figure 2, bridge area size of 0.5mm × 0.5mm, included angle θ At a 45 ° angle, the ignition sensitivity of TaN thin film energy exchange elements under different bridge shapes was studied by dividing the middle part of Figure 2 equally. The shape of the bridge area divided equally by Figure 4 (Figure 3) is shown in Figure 6.

        The ignition sensitivity test results of energy exchange elements with different equally divided bridge areas are shown in Table 4. The results in Table 4 indicate that under the same bridge film thickness, bridge area size, and bridge area angle, when the middle part of the bridge area is equally divided into 8, the average ignition voltage is the lowest, at 11.9V; When the score of the bridge area increases to 30, the bridge area lines are prone to breakage and other phenomena. The actual measured values of the lines have a large error compared to the design values, and the process yield is not high. Based on the manufacturing process level and ignition sensitivity test results, the optimal score for bridge zone is between 4-8.

Figure 6 Schematic diagram of the 4-way division of Figure 2 in the bridge area (Figure 3 in the bridge area)

Table 4 Test results of ignition sensitivity of energy exchange elements divided equally in different bridge areas

        Based on the above research, further optimize the bridge area shape and select a bridge membrane thickness of 0.9 μ m. Bridge area size 0.5mm × 0.5mm, with an angle of 45 °, the bridge area is divided equally into 4. A sawtooth shape has been added to Figure 3 of the bridge area shown in Figure 6, as shown in Figure 7.

Figure 7 Schematic diagram of optimized bridge area graphics

        After optimization, there are 6 types of bridge area graphics, with 4 sawtooth numbers and 90 ° sharp angles in the bridge area graphics; The zigzag number of Figure 5 in the bridge area is 4, with a sharp angle of 60 °; Bridge area figure 6 has a sawtooth count of 10 and a sharp angle of 60 °; The zigzag shape of Figure 7 in the bridge area is square, with a number of zigzags of 4; The zigzag shape of Figure 8 in the bridge area is semi-circular, with a number of zigzags of 4; The zigzag shape of Figure 9 in the bridge area is trapezoidal, with a number of zigzags of 4; In Figure 4, 5, 7, 8, and 9 of the bridge area, the sawtooth spacing is the same on the left and right, as well as the spacing between the top and bottom. The test results of the ignition sensitivity of energy exchange elements with different bridge shapes after optimization are shown in Table 5. The results in Table 5 indicate that, under the same thickness and bridge area size, the ignition voltage of the serrated shape (bridge area Figure 4, bridge area Figure 5, bridge area Figure 6) is lower than that of the non serrated shape before optimization. The ignition voltage of the serrated shape with a sharp angle of 60 ° (bridge area Figure 5) is lower than that of the serrated shape with a sharp angle of 90 ° (bridge area Figure 4); The firing voltage of bridge zone shapes 7, 8, and 9 is similar, with a slightly higher firing voltage than that of bridge zone shape 3 (bridge zone is divided into 4), indicating that the sawtooth shape is flat or semi-circular, which hinders the passing current.

Table 5 Test results of firing sensitivity of energy exchange elements in different bridge area shapes after optimization

2.5 TaN thin film transducer firing voltage

        Based on the above research results, four schemes were designed for low-energy experimental verification, as shown in Table 6. The ignition sensitivity test results of TaN thin film transducer are shown in Table 7. The test results in Table 7 show that from Scheme 1 to Scheme 4, the ignition voltage gradually decreases, and the average ignition voltage of Scheme 3 and Scheme 4 drops below 5V.

Table 6 Test scheme for ignition sensitivity of TaN thin film transducer

Table 7 Test results of ignition sensitivity of TaN thin film transducer

3 Conclusion

        This study is based on the excellent electrical properties of TaN and uses MEMS technology to prepare TaN thin film energy exchange elements. The influence of bridge film thickness, bridge region pattern and size on the ignition sensitivity of microstructure energy exchange elements was studied, and the following conclusions were obtained:

       (1) When the shape and size of the bridge region are constant, as the thickness of the bridge film increases, the firing voltage of the TaN thin film transducer decreases first. When the thickness of the bridge film increases to a certain extent, the firing voltage of the transducer tends to increase again. The thickness of the bridge membrane is 0.9 μ At m, the ignition voltage is the smallest.

       (2) The shape of the bridge zone has a significant impact on the firing voltage of TaN thin film transducer. This article designs a bridge membrane with an overall shape of "I" shape through a series of graphic studies, when the angle between the bridge area is θ When the angle is 45 °, the bridge area is divided into 4 equal parts, the number of serrations is 4, and the serration angle is 60 °, the firing voltage of the transducer is lower than 5V, achieving the goal of low energy TaN thin film transducer.