(Invited) Reactive Bonding with Integrated Reactive and Nano Scale Energetic Material Systems (iRMS): State-of-the-Art and Future Development Trends

The latest trends in micro systems technology focus on the integration of new materials, such as metals or polymers, in a smart system [1]. Furthermore, most of the Micro-Electro-Mechanical-Systems (MEMS) devices need strong and hermetically sealed packages, which guarantee a reliable functionality [2]. In general, the hermetic MEMS packaging is done by wafer bonding, such as glass-frit and anodic bonding [3]. These bonding procedures operate at high bonding temperatures where all components are heated up. This can cause damage to temperature sensitive components. One possible solution to reduce the bonding temperature is the so called reactive bonding. This technique uses an internal heating produced in reactive and nano scale energetic material systems (RMS) [4]. Nevertheless, the main principle behind these nano energetic materials is that at least two nano scale educts (in our case A and B) undergo exothermic intermixing to form products. This heat is produced in form of a self-propagating exothermic reaction (SER). This paper focuses on the integration of the RMS, so called iRMS. We will demonstrate different types of iRMS, ranging from multilayered systems to particles and vertical systems, as well. An overview of the iRMS types used in this study can be found in Figure 1. It will be shown that the multilayered iRMS particularly the physical vapor deposited (PVD-iRMS), can be used for highly efficient and reliable wafer bonding. Therefore, we have bonded different wafer types and materials at room-temperature. We have shown, that solder layers as well as surface pre-treatment is not needed for bonding anymore. In addition to that we have bonded and characterized different types of demonstrators. Figure 2 shows a bonded MEMS pressure sensor onto a ceramic substrate.  In addition to that, we will demonstrate that the electro-chemical deposition (ECD), such as the water based electrolytes (WB-iRMS) and ionic liquids (ioLi-iRMS) are new innovative and more cost efficient deposition techniques for multilayered iRMS. Herein, we developed single bath electrolytes, where two educts are in one electrolyte. With a defined current/density signal educts A and B were deposited, respectively. Figure 3 shows these deposition results using WB-electrolytes.  Via SEM- as well as EDX-analysis we have investigated that depending on the applied potential different surface morphologies and educt A/B ratios could be achieved, respectively. Based on these results we have successfully deposited individual layers with a high purity and we were able to stack A and B layer as WB-iRMS. Contrary to the state-of-the-art multilayer approach we will show new iRMS deposition methods. These two are iRMS deposited via aerosol jet (AJ-iRMS) and vertically arranged iRMS (V-iRMS). Figure 4 shows first results for V-iRMS. It has been demonstrated that different geometries are suitable for V-iRMS (such as meander structures, cf. Figure 4a). In addition to that nano pattering with high aspect ratios (Figure 4b) as well as the deposition of educt B inside the geometries was possible (Figure 4c). Furthermore, we will show basic and boundary process conditions for the deposition of AJ-iRMS and V-iRMS. References

[1]    Gessner, T.: Smart Systems Integration 2011; VDE Verlag; 2011.

[2]    Ramm, P. et al.: Handbook of Wafer Bonding; Wiley-VCH, 2012.

[3]    Niklaus, F. et al.: J. Appl. Phys., 99, 091101, 2006.

[4]    Braeuer, J. et al.: Sensors & Actuators A 188, pp. 212-219, 2012.