Batch fabrication of polymer microsystems with shape memory microactuators
This paper introduces the technologies of ultrasonic welding and heat-activated bonding for batch integration of micromachined polymer layers and shape memory alloy (SMA) foils or films. A series of ultrasonic welding tests is performed to achieve matter-free bonds on the wafer level with vertical accuracy of 1 mum. Heat-activated bonding is tested for various pressure and temperature conditions using micromachined foils of 60 mum thickness. The technologies are combined in a new process flow for batch fabrication of mechanically active polymer microsystems. The process flow is validated by the fabrication and characterization of SMA-actuated polymer microvalves.
A bistable SMA microvalve for 3/2-way control
Abstract In this paper the layout, fabrication, and characterization of a first-of-its-kind bistable 3/2-way shape memory microvalve are presented. A symmetric arrangement of two counteracting shape memory alloy (SMA) microbridges is used for switching. The stable states in power-off condition are realized by magnetostatic contact forces between a movable hard-magnetic cylinder and two soft-magnetic layers. A detailed design study of the magnetic retaining system is performed to meet the requirements of a large pressure range and identical flow rates in the open valve state and a low leakage in the closed valve state in both outlet ports. The overall dimensions of first demonstrators are 11 mm × 6 mm × 4 mm. The 3/2-way bistable microvalve performance is demonstrated, showing identical flow rates in both outlet ports for a pressure difference up to 200 kPa for gas (N2) and up to 100 kPa for liquid (water) with flow rates of 1250 sccm and 11 ml/min, respectively.
Entwicklung und Herstellung einer chemisch inerten Mikropumpe
A chemical inert, polymeric and piezo-driven micro pump was developed and fabricated. The ultrasonic welding, as a monolithic bonding method, was applied to the micro polymeric components of the pump. The main components of the pump, including an actuator unit and a valve unit with two valves, were separately developed and welded using ultrasonic welding. The pump is driven by a disc-shaped, piezoelectric bending actuator, which consists of a piezo disc and a passive disc. Two types of the passive disc, a metal disc and a polymeric disc, were investigated with regard to the deflection of the bending actuator. Endurance tests revealed that, polymer was not suitable material for the passive disc of the bending actuator because of creepage phenomena. Different thermal-expansion coefficients of materials (piezo ceramic, steel and polymer) resulted a deformation of the actuator under different temperatures. Among various structures of valves, a valve with a free-moving membrane was chosen for the pump. To be handled more ergonomically as well as to reduce the amount of pieces,, two valves required in the pump were integrated into one valve unit. The valve stroke, which was determined by the height of the valve chamber, is regarded as critical parameter for the pump performance. With an optimal valve stroke of 30 μm, a pump performance, a maximal flow rate of 3 ml/min and a maximal back pressure of 750 hPa have been achieved. The pump was tested for over 1800 hours, with a continuous operation of over 320 million pump cycles, without fatigue appearance. A climatic test showed that, the performance of the pump was not influenced by the relative humidity (measured from 10 to 90%), and the performance remained stable up to 30°C, and deteriorated with higher temperature because of the deformation of the actuator. A higher glue temperature for the actuator or other material for passive element of the actuator with similar thermal expansion coefficient as piezo ceramic could enlarge the operational temperature range, in which the pump performance is stable.