Alexis Debray

Alternative approach in 3D MEMS-IC integration using fluidic self-assembly techniques

Nowadays, industries are investigating new, original and appropriate solutions to address challenges in 3D MEMS-IC large-scale integration. Self-assembly techniques are among those. We report on an alternative approach inspired from fluidic self-assembly and using the flip-chip method. Here, solder bumps are directly formed onto a MEMS chip using liquid solder solution in a bath. The self-alignment process is operated after surface treatment by plasma deposition to form high and low wettability selective patterns. Finally, MEMS and electronic chips are permanently bonded after low thermal heating without any pressure. Electrical contact is established and electromechanisms of the microsystems are proven. Compared to classic MEMS-IC flip-chip methods, this strategy presents many advantages: it is a low-cost and fast fabrication process requiring no specific equipment for deposition of solder bumps. Furthermore, it can be applied on different substrates and it does not require a specific pressure method during the bonding process. This strategy is also an appropriate fabrication method for large-scale MEMS integration where electronic connection density is high.

A passive micro gas regulator for hydrogen flow control

This paper presents the design, fabrication process, experimental characterizations and simulations of a novel passive micro gas regulator. The device is to be used in a miniature fuel cell for portable electronic applications in order to regulate the hydrogen flow feeding the fuel cell from a high-pressure tank. Its structure and working principle are similar to some macroscopic devices. Using MEMS technologies, e.g., deep-RIE etching and multiple wafer bonding, the dimensions of the device have been made less than 8 × 8 × 1 mm3. Moreover, as it is passive, it consumes no power from the fuel cell. Thanks to these two features, it is well suited for portable applications. To our knowledge, this is the first passive micro gas regulator, except those actuated by hydrogels. The experimental characterization shows that the opening and closing are controlled by the released gas pressure. Up to an input pressure of 8 atm, the device has been successfully driven and the leakage has been measured to be below 0.1 sccm nitrogen. Analytical models for the moving part and for the flow rate show a good agreement when compared to the experimental data.

A low melting point alloy as a functional material for a one-shot micro-valve

A one-shot valve made using MEMS (micro-electro-mechanical systems) technologies has been designed, fabricated and characterized. The operation of the device is temperature and pressure dependent. It consists in a channel obstructed by a membrane coated with a low melting point alloy. The valve is normally closed and opens if the ambient temperature is higher than the melting temperature of the alloy and if the pressure difference across the channel is such as to fracture the membrane. The working principle of the device has been demonstrated and several characteristics have been measured.

Fluidic self-alignment applied to a micro-fluidic system

A technique for the self-alignment of components is applied to the assembly of a passive micro-valve which is to be used for safety purposes in a miniature fuel cell. The technique uses the capillary forces originating in the interactions of HMDS (Hexadimethyldisilazane) and the faces of the components to achieve their passive alignment. HMDS is chosen because it is a volatile, low surface tension and inert liquid. The originality of this method is that the liquid area is defined by the edges of the components. Compared to a traditional pick-and-place technique, it leads to a leakage rate more than five times smaller.

3-D Large-Scale IC/MEMS Co-Integration Using Liquid Solder for Flip-Chip Assembly

In this paper, we discuss a flip-chip packaging method using liquid solder for 3D large-scale electronic/MEMS co-integration. This approach has been inspired from self-assembly technique which is emerging as one of the main methods for fabrication of heterogeneous micro-and nano-systems. We proposed to form solder bump by coating liquid solder directly on electrodes of a MEMS chip based on sophisticate microstructures of electrostatic microactuator array. Self-alignment and assembly techniques for electronic receptor chip were also detailed in order to achieve efficient flip-chip of MEMS and Electronic chip without any stiction and contamination problem. Functionality of the system has been validated and perspectives discussed.

Thermal modification of the rigidity of micro-structures by the phase transition of a fusible alloy

An original micro-valve has been designed, modeled, fabricated and characterized. Its novelty resides in the thermal modification of the rigidity of its movable element by the phase transition of a fusible alloy integrated by self-assembly onto a silicon membrane. It is applied as a purge and safety valve for hydrogen micro fuel cells. The experimental results demonstrate the modification of the rigidity of the mechanical structure by melting and freezing one of its constituents, a property favored at a small size. This principle allows one to latch a mechanical element in the open and closed positions, as well as for ambient temperature sensing. Its potential applications include other devices such as electrical relays and optical switches, and can be integrated with active materials.