This invention addresses the general problem of motive power for micromachines, i.e., those mechanical devices whose individual components are typically between 1 .mu.m and 1000.mu.m in size. The essence of the current invention is the introduction of gas pressure-driven pistons which use capillary forces to seal the working fluid in the working device and to transmit the forces which result from the pressure acting on the working fluid to the piston. The result is a new class of microminiature linear activators which make available piston forces some 2-3 orders of magnitude larger than do conventional electrostatic microactuators at similar operating voltages.
In the field of micromechanical technologies, there is a great need for devices which can provide useful work to active micromechanical assemblies. (For the purposes of this application, an active micromechanical assembly would be a micromachine having driven moving parts, for example a gear train, whereas a passive micromechanical assembly would depend on the deformation of fixed elements, such as cantilevers, in response to external motion or other external conditions.) The same need is commonplace on the macroscopic scale; an assembly of gears and pivots and linear motion guides is not a lathe until some source of motive power is added. On the macroscopic scale such motive power is often provided by internal and external combustion engines, although the energy provided by these sources may first be transformed into forms useable by electric motors or hydraulic actuators, which devices may directly drive the desired assembly.
Unfortunately, the standard macroscopic sources of motive power do not scale well into the microscopic regime with which we are currently concerned. They are either too complicated to manufacture at such dimensions or the physical laws that govern their operation do not scale favorably, resulting in inadequate performance. Several types of motive power have been investigated in the prior art for application in the microscopic regime, notably electrostatic motors, piezoelectric drives, and thermal bimorphs, and these have proven useful in some cases. In general, however, the force produced is limited, and/or is available over a rather small range of linear displacement, and hence is not adequate for a large number of potential applications. Further, some of the available options (piezoelectric drives, thermal bimorphs, and others) do not adapt easily to integrated circuit processing techniques, an important factor for applications requiring many actuators or when many complete mechanisms must be built.
For the foregoing reasons, there is a need for a new type of microminiature linear activator that provides accessible work per operating cycle (force x length of stroke) vastly greater than is achievable using currently available microscopic actuators. A further need is for such a device that is easily manufactured in large quantities on a silicon wafer (the current arena for development of micromachines) using fabrication techniques compatible with the enormous suite of techniques developed for fabrication of integrated circuits.