An example embodiment of the present invention relates to microelectromechanical system (MEMS) switches and, more particularly, to a MEMS switch with a liquid dielectric.
Typical transistors, such as complementary metal-oxide-semiconductor (CMOS) switches, have advantages such as small size and speed. However, the smaller and faster the switch, the more the transistor may suffer leakage. Transistors also are unreliable in extreme temperature or pressure conditions, such as space and mining applications. Further, transistors cannot handle high voltage without suffering transistor shoot-through.
Typical MEMS switches have many advantages compared to solid state CMOS switches, including very high ON/OFF ratios, very low power consumption, and excellent input/output isolation. These advantages allow MEMS switches to be used in many applications, including reconfigurable antennas and circuits, which in turn are used in radar, communication, and instrumentation systems. However, mechanical switches traditionally suffer from high pull-in voltages and slow response. These limitations have prevented the use of MEMS switches in a wide range of applications. MEMS switches utilizing low voltage also suffer from significant leakage.
Many efforts have been made to improve the MEMS switch response by applying new structures and materials. In general, the concept behind electrostatic MEMS switches is to engineer a parallel plate capacitor to create an actuation force, hence switching ON or OFF. The net force applied to the parallel plate is the difference between the electrostatic force and the structural damping force, which is defined as
where
Cp represents the parallel plate capacitance, d represents the gap separation between the parallel plates, d0 represents the gap at rest, ε0 represents the permittivity of air, εr represents the permittivity of the gap filling material, Vd represents the applied voltage, and k represents the spring constant of the switch moving part. Based on equation (1), the actuation force at a given applied voltage can be enhanced either by reducing the spring constant of the switch or by increasing its parallel plate capacitance. The first approach can be achieved using techniques, such as by engineering new structures with lower spring constant or by using more flexible materials to fabricate the switch-moving parts.
The second strategy to decrease the actuation voltage is by increasing Cp to enhance the electrostatic force. According to equation (1), this can be achieved by increasing the area, reducing or reshaping the air gap, or using a high εr filling material. The gap thickens as a technology dependent parameter. Increasing the area will reduce the density and yield of the fabricated device. Moreover, εr cannot be increased by using a common rigid dielectric, because doing so would prevent actuation of the switch by blocking its moving part.
A MEMS switch and method of fabrication thereof are provided in accordance with example embodiments described herein. In a first set of example embodiments, a microelectromechanical system switch is provided that includes a cantilevered source switch, a first actuation gate disposed parallel to the cantilevered source switch, a first drain disposed parallel to a movable end of the cantilevered source switch, and a liquid dielectric disposed within a housing of the microelectromechanical system switch.
In some embodiments, the liquid dielectric fills at least a portion of a volume between the cantilevered source and the first actuation gate. In some embodiments, the first drain is disposed outside the liquid dielectric. In some embodiments, the microelectromechanical system switch also includes a second actuation gate, wherein the first and second accusation gates are disposed on opposite sides of and parallel to the cantilevered source switch. In some embodiments, the microelectromechanical system switch also includes a second drain, wherein the first and second drains are disposed on opposite sides of and parallel to the movable end of the cantilevered source switch.
In some embodiments, simultaneous activation of the first and second actuation gates causes the cantilevered source switch to maintain an unactuated position. In some embodiments, the first drain and second drain are electrically shorted. In some embodiments, the liquid dielectric is water. In some embodiments, the liquid dielectric is one of water, gasoline, hydrazine, ethanol, olive oil, or acetic acid. In some embodiments, the microelectromechanical system switch satisfies an XOR logic, in an instance in which the first and second actuation gates are electrically connected to first and second input logic gate.
In another set of example embodiments, a method of fabricating a microelectromechanical system switch is provided. In such embodiments, the method includes providing a cantilevered source switch, providing a first actuation gate disposed parallel to the cantilevered source switch, providing a first drain parallel to a movable end of the cantilevered source switch, and providing a liquid dielectric disposed within a housing of the microelectromechanical system switch.
In some embodiments of the method, the liquid dielectric fills at least a portion of a volume between the cantilevered source and the first actuation gate. In some embodiments of the method, the first drain is disposed outside the liquid dielectric. In some embodiments, the method also includes providing a second actuation gate, wherein the first and second accusation gates are disposed on opposite sides of and parallel to the cantilevered source switch.
In some embodiments, the method also includes providing a second drain, wherein the first and second drains are disposed on opposite sides of and parallel to the movable end of the cantilevered source switch. In some embodiments of the method, activation of the first and second actuation gates causes the cantilevered source switch to maintain an unactuated position. In some embodiments of the method, the first drain and second drain are electrically shorted. In some embodiments of the method, the liquid dielectric is water. In some embodiments of the method, the liquid dielectric is one of water, gasoline, hydrazine, ethanol, olive oil, or acetic acid. In some embodiments of the method, the microelectromechanical system switch satisfies an XOR logic, in an instance in which the first and second actuation gates are electrically connected to first and second input logic gates.
Having thus described example embodiments of the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:
Some embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, various embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout.
In an example embodiment, a new MEMS switch and a method of fabricating the new MEMS switch are provided. The MEMS switch may utilize a liquid dielectric which may increase the capacitance of the switch rather than using the liquid as a conducting medium. Further, the dielectric may reduce the pull-in voltage of the liquid dielectric MEMS switch. In an example embodiment, a lateral dual-gate MEMS switch with liquid dielectric may reduce pull-in voltage by greater than 8 times to become as low as 5.36V.
In some examples embodiments, the liquid dielectric MEMS switch may be configured as a single switch XOR logic gate, which may significantly reduce its required area.
Liquids have a relativity high permittivity compared to gases and allow mechanical parts to move. These properties enable liquids to be used as flexible dielectrics in the MEMS domain. The usage of a liquid as a flexible dielectric may reduce the actuation voltage of electrostatic MEMS switches. Based on equation (1), the actuation voltage is inversely proportional to the square root of the parallel plate capacitance, as illustrated in equation 3 below.
Hence, the actuation voltage is inversely proportional to √{square root over (εr)}. Table 1 shows the relative permittivity for different liquids and gases. In addition, Table 1 shows the theoretical reduction in the actuation voltage based on equation 3.
Liquid dielectric shortfalls, such as stiction, surface tension and damping may be addressed by the design of the liquid dielectric MEMS switch. For example, stiction may be avoided by limiting or preventing contact between solids, e.g. source and drain, in the liquid environment. In some examples, this is achieved by designing the MEMS structure such that all of its contact point areas are outside the liquid volume. Particular structural designs, some of which may have dual gates as described below, may neutralize the surface tension. Finally, damping may be affected by the choice of liquid and the fill level of the dielectric.
A liquid dielectric MEMS switch and method of manufacture thereof are provided in accordance with an example embodiment.
The depicted example embodiment is directed toward a dual gate liquid dialectic MEMS switch, although other configurations are contemplated as well, such as a single actuation gate liquid dielectric switch.
The source 104 may be a cantilevered source switch that, in some embodiments, may be anchored at one end. An actuation gate 106 may be disposed in parallel with the cantilevered source switch 104. A drain 108 may be disposed in parallel with the cantilevered source switch 104 near the end of the movable portion. The void between the cantilevered source switch 104, actuation gates 106 and drains 108 may create a moving channel. The moving channel may be filled with a liquid dielectric. The liquid dielectric may be gasoline, acetic acid, olive oil, ethanol, hydrazine, glycerin, water, or any other liquid dielectric with suitable permittivity.
In an example embodiment, the liquid dielectric level is filled below the drain contacts as depicted in
In an example embodiment of the liquid dielectric MEMS switch 100 with dual actuation gates 108, each of the actuation gates may be electrically connected to a different logic input and the drains 108 may be shorted together, as depicted in
The cantilevered source switch 104, actuation gates 106, and drains 108 may be made from a suitable conductive material, and in this regard may comprise any MEMS-compatible material. In one example embodiment, these elements may be made from any MEMS-compatible material. In one example embodiment, these elements may be made of gold. Similarly, the dimensions of the cantilevered source switch 104 may also vary in accordance with design goals. For instance, in an example embodiment, the cantilevered source switch 104 dimensions may be 100 μm×20 μm×3 μm and a gap of 3 μm is left below the cantilevered source switch to enable its movement and to allow for liquid dielectric 110 filling. In this example embodiment, the actuation gates 106 may each have a 90μ×24 μm surface area and the parallel plate area between each actuation gate and the cantilevered source switch may be 90 μm×20 μm. The gap between each actuation gate and the cantilevered source switch 104 may be 1 μm and is reduced to 0.5 μm between the cantilevered source switch and the drain 108. The drain 108 may act as a mechanical stop, preventing shorting between the cantilevered source switch 104 and the actuation gates 106.
It should be understood that the dimensions of this example embodiment are provided for illustrative purposes and other dimensions may be used in other example embodiments.
Referring back to the example dimensions of
C
gc=0.065LW−0.137 [pF], for LW≥4 μm, (4)
where LW is the liquid dielectric 110 level in micrometers.
The increase in Cgc may be translated into an increase in the cantilevered source switch 104 actuation for a given voltage, or in other words a reduction in the required pull-in voltage.
A significant decrease in pull-in voltage may be achieved using a liquid dielectric 110 level as low as 5%. This result may be consistent with the gate-source capacitance discussed above in
Referring now to
As shown in block 804 of
As shown at block 806 of
Alternatively, as shown at block 808 of
In an example embodiment, the first and second actuation gates may be electrically connected to first and second input logic.
As shown at block 810 of
As shown at block 812 of
In an example embodiment, the liquid dielectric 110 may be provided to the liquid dielectric MEMS switch 110 through a gap below the cantilevered source switch 104. The gap acts as a microfluidic channel. Additionally, the gap between the cantilevered source switch 104 and the actuation gates 106 may have a capillary effect, which may draw the liquid dielectric 110 level up.
Additionally or alternatively, the liquid dielectric 110 may be provided to the liquid dielectric MEMS switch 100 by condensing a liquid dielectric vapor into the liquid dielectric MEMS switch 100. Condensation of a liquid dielectric vapor may allow the liquid dielectric to easily fill narrow parts of the liquid dielectric MEMS switch 100.
As shown at block 814 of
In an example embodiment of the liquid dielectric MEMS switch 100 with electrically shorted drains 108 and first and second actuation gates electrically connected to first and second logic input, the liquid dielectric MEMS switch may satisfy a XOR logic or truth table. The cantilevered source switch 104 may be substantially centered when not actuated and might not be in contact with the drain 108. In an instance in which an actuation gate 106 is activated, the cantilevered source switch may make contact with the drain 108. In an instance in which both actuation gates 106 are activated simultaneously, the cantilevered source switch may remain in the substantially centered position.
The utilization of a liquid dielectric in a MEMS switch may reduce the pull-in voltage of the MEMS switch, therefore allowing smaller switches to be used with lower voltage supplies and lower power consumption. The liquid dielectric MEMS switches may be used in a variety of applications, such as those in which transistors are too fragile and traditional MEMS switches are too large. Some example settings for liquid dielectric MEMS switches are space and mining.
As described above,
Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2016/053504 | 6/14/2016 | WO | 00 |
Number | Date | Country | |
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62175396 | Jun 2015 | US |