US20150129399A1

US20150129399A1 - Devices with liquid metals for switching or tuning of an electrical circuit

Info

Publication number: US20150129399A1
Application number: US13/981,954
Authority: US
Inventors: Shai Feldman; Oren Aharon
Original assignee: Kadoor Microelectronics Ltd
Current assignee: Kadoor Microelectronics Ltd
Priority date: 2012-02-15
Filing date: 2012-07-31
Publication date: 2015-05-14
Also published as: US9012254B2; WO2013121254A1; WO2013121253A1; US20140017842A1

Abstract

Devices for switching or tuning of an electrical circuit comprise a liquid metal (LM) drop confined inside a sealed cavity. The cavity is formed at least partially inside a microelectronics layered structure which includes metal, dielectric and semiconductor layers. The microelectronics layered structure may be prepared using a VLSI/CMOS technology. Some of the VLSI/CMOS metal layers or metalized vias may be used for conduction lines contacted by the LM drop or as RF transmission lines opened or closed by the LM drop.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and hereby claims the priority benefit of commonly-owned and co-pending U.S. provisional patent applications No. 61/685,113 filed Mar. 12, 2012, No. 61/633,624 filed February 15, No. 61/633,625 filed Feb. 15, 2012 and No. 61/685,886, filed Mar. 27, 2012, all of which are incorporated herein by reference in their entirety.

FIELD

Embodiments disclosed herein relate in general to devices using liquid metal (LM) drops and in particular to microelectronic or MEMS devices incorporating miniaturized LM drops.

BACKGROUND

The use of liquid metals in various electrical or electromechanical devices is known. Larger devices using liquid metals include relays (e.g. mercury relays) and switches. Small LM volumes (“drops”) are also known for their use in micro-electro-mechanical system (MEMS) devices, for example for RF and other switching and cooling devices. However, in order to use LM components, such devices have added structural features (e.g. layers) which are not needed in regular MEMS devices. In addition, the incorporation of LM drops in microelectronic devices requires added layers and technological process steps.
There is therefore a need for, and it would be advantageous to have devices for switching or tuning of an electrical circuit based on standard microelectronics and/or MEMS technologies which incorporate LM drops.

SUMMARY

In various embodiments, there are provided devices for switching or tuning of an electrical circuit having a liquid metal drop enclosed and sealed inside a small cavity. The term “drop” is used to describe an entity having a volume made of LM, and is not meant to be limiting to a particular shape or size. In some embodiments, the drop may have a very small (miniaturized) volume, on the order of a few cubic micrometers. In other embodiments, the drop may have a volume of tens of cubic micrometers or more. The drop may be enclosed and sealed in a cavity of slightly larger volume (referred to herein as “sealed cavity” or “sealed volume”). In some embodiments where the drop has such a miniaturized volume, the cavity sealing it may be formed in a microelectronic or a MEMS device (including glass based MEMS), or in a microelectronics based interposer for 2.5D and/or 3D multiple IC integration. In such embodiments, the small total thickness of microelectronic layered structure prepared by planar technologies (generally less than 10 micrometer) may restrict the LM drop size.
In some embodiments, the sealed volume is defined at least partially by microelectronics (e.g. VLSI CMOS) device layers. In other words, its boundaries are defined by layers or features of a microelectronics process or technology (such as VLSI-CMOS). The term “CMOS” is used henceforth as an exemplary (but in no way limiting) term for the processes or technologies (e.g. RF-CMOS, Silicon, Glass, GaAs or GaN), to simplify the description. In other embodiments, the sealed cavity may be formed by covering and sealing a LM drop formed on a flat surface. In yet other embodiments, the sealed volume may be defined by MEMS layers (e.g. between bonded wafers or inside deep silicon trenches)
The LM drop may physically open or close a RF transmission line and therefore open or close an electrical circuit by a force applied to the LM drop, which force creates a change in the liquid metal shape and dimensions. The electrical circuit under open or close states may be a RF circuit but could also be a DC, AC or THz circuit. The switching may occur directly between open and close states or through any number of intermediate states.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments are herein described, by way of example only, with reference to the accompanying drawings, wherein:

FIG. 1A shows in cross section an embodiment of a device 100 for RF switching using a LM drop in an open state;

FIG. 1B shows in cross section device 100 with different top view section markings;

FIG. 1C shows a top view through section A-A of device 100;

FIG. 1D shows a top view through section B-B of device 100;

FIG. 1E shows a top view through section C-C of device 100;

FIG. 1F shows in cross section device 100 in a closed state;

FIG. 1G shows a top view through section B-B of device 100 in the closed state;

FIG. 2A shows in cross section an embodiment of a device 200 for RF switching using a LM drop in an open state;

FIG. 2B shows in cross section device 200 in a closed state;

FIG. 3A shows in cross section an embodiment of a device 300 for DC or AC switching using a LM drop in an open state;

FIG. 3B shows a top view through section A-A of device 300;

FIG. 3C shows in cross section device 300 in a closed state;

FIG. 4A shows in cross section an embodiment of a device 400 including a LM drop and used as a variable capacitor for RF switching in a first state;

FIG. 4B shows in cross section device 400 in a second state;

FIG. 5A shows in cross section yet another embodiment of a device 500 for RF switching using a LM drop in an open state;

FIG. 5B shows device 500 in a closed state;

FIG. 6 shows schematically in top view through an appropriate section an embodiment of a 1×N switch using devices as in any embodiment in FIGS. 1-5.

DETAILED DESCRIPTION

FIG. 1A shows in cross section an embodiment of a device 100 for RF switching using a LM drop in an open state. Top views of device 100, taken through sections marked A-A, B-B and C-C are shown respectively in FIGS. 1C, 1D and 1E. FIG. 1F is a cross sectional view of device 100 in a closed state, while FIG. 1G shows a top view taken through a section B-B of device 100 in the closed state. Device 100 may be for example a switch which is used to open or close communication channels of a band selection circuit located in a high frequency communications system where the switching element is the LM drop. In an embodiment, switching may be performed between different communication bands of a RF communication system. In an embodiment, switching or tuning of RF power amplifiers may be performed between different RF bands. In an embodiment, switching may be performed between transmit and receive states of a RF communication system.
Device 100 includes a LM drop 102 located inside a sealed cavity 104. As shown (FIG. 1B), cavity 104 is defined by a bottom plane 104 a, side planes 104 b, 104 c (each number referring to one side “wall” and one back or front wall of the cavity when looking at the cross section) and a top plane 104 d. Note that the cavity need not have a rectangular cross section, and may have other cross section shapes. In an embodiment, cavity 104 is formed partially inside a layered structure processed by using silicon microelectronics technology, exemplarily a VLSI-CMOS process. In other embodiments, for example as in device 100, the cavity may be formed entirely inside the microelectronics layers structure. In device 100, the cavity side planes 104 b, 104 c are bound by CMOS metallic layers 106 a-d, CMOS dielectric layers 108 a-c and 110 and CMOS vias (interconnects) 112.
The cavity is sealed by a CMOS sealing layer 116 (i.e., in this embodiment, cavity top plane 104 d is covered by sealing layer 116). Thus, unlike known LM-containing sealed cavities which are either defined by glass tubes or by two wafers, a sealed cavity disclosed herein is defined from all sides either partially or fully by CMOS (microelectronics) layers. Methods and processes for forming a LM drop inside a sealed cavity in microelectronics layers are described in detail in co-pending PCT application PCT/IB2012/XXXXXX by the same inventors, which is incorporated herein by reference. In an embodiment and as described therein, the LM drop is an alloy of about (by weight) 68.5% gallium (Ga), 21.5% indium (In) and 10% tin (Sn). As described in PCT/IB2012/XXXXXX, the Ga—In—Sn alloy may have small amounts of added metals which affect the formation of the LM drop. In some embodiments, the amounts may total less than 1% by weight.
Device 100 further includes a first RF transmission (“signal”) line 118 which extends between a first end 120 and a first contact point 122 through a via 118 a and a second RF transmission (“signal”) line 124 which extends between a second end 126 and a second contact point 128 through a via 124 a. As shown in section A-A in FIG. 1C, ground lines of 162, 164 are provided for signal line 124 (e.g. as a coplanar waveguide—CPW) and ground lines 166, 168 are provided for signal line 118. As shown in section B-B in FIG. 1C, a dielectric layer 146 is supplied in the same plane as that of metallic layer 106 c. Device 100 also includes a first conduction line 130 which extends between a first end 132 and a second end 134 through a via 130 a and a second conduction line 136 which extends between a first end 138 and a second end 140 through a via 136 a. In an embodiment, the conduction lines are connected to a direct current (DC) source. In another embodiment, the conduction lines are connected to an alternating current (AC) source. LM drop 102 is in permanent electrical contact with second end 140 and is electrically isolated from conduction line 130 by dielectric layer 110.
The substrate (e.g. Si) areas below the CMOS layered structure are isolated by N or P well (tap) guard rings to isolate the RF transmission lines 118 and 124. The guard rings may be single, double or triple ground rings, and may be formed using design rules familiar in the CMOS technology. In an embodiment, a guard ring 150 may be located under a contact area, therefore isolating for example areas 158 and 160 located respectively under RF transmission line 118 and RF transmission line 124. However, the guard ring location may be anywhere in the design in order to improve the isolation between different RF elements of the switch. Other guard rings 152, 154 156 may also be located around the entire switch area (152, 154) and underneath it (156) in order to isolate it from the surrounding signals in the CMOS circuits.
The contact metals may be specifically chosen not to react with the LM. For example, tungsten (W) is both CMOS compatible and does not react with a Ga—In—Sn alloy or with mercury (Hg). Tungsten can therefore serve as a contact metal in a device such as device 100.
The dielectric layers in contact with the LM drop are part of the VLSI-CMOS dielectric layers. An exemplary CMOS compatible dielectric layer material which does not react with a Ga—In—Sn or Hg LM drop is SOG (Spin on Glass). Another exemplary CMOS compatible dielectric material which does not react with a Ga—In—Sn LM or with Hg is alumina. Alumina can also be deposited over all the internal surfaces of the cavity before the LM drop is formed. Alumina creates a high wetting angle with the LM drop (needed for lower operation voltage), has high breakdown voltage and high dielectric constant.
In some embodiments, first type “wetting” layers may be formed inside the sealed volume to increase the wetting angle between the LM drop and the layers it is in contact with. Such first type wetting layers may be needed for lower operation voltage. They include for example self assembled monolayers (SAM) of Alkoxy-silanes, Chloro-silanes or Flouro-silanes. In some embodiments, second type wetting layers may be formed inside the sealed volume to hold the drop in location in order to prevent its movement under acceleration, shock or vibration, by fixing drop surfaces not intended to be moved to the inner side of the cavity. Such layers include for example SAM of 11-hydroxy-1-undecanethiol, poly(dimethyl siloxane). The wetting layers may be patterned inside the sealed cavity
In use, in the “open” state, FIG. 1A, LM drop 102 has a left “front” 144 which does not contact first contact point 122 of first RF electrode 118. Therefore, RF transmission cannot be performed by the device. Exemplarily, an electrostatic force can be applied on the LM drop through a designated voltage applied between the two DC electrodes. Under an applied electrostatic force, the drop changes its shape, FIG. 1F, such that its left front 144 contacts first contact point 122, therefore closing the transmission line and enabling the transmission of the RF signal through the switch. This represents the “closed” state. When ground lines 166, 168 are connected to signal line 118 (not shown), the RF signal in closed state is actually transferred to the ground lines of the switch. This represents a “closed and grounded” state. The electrostatic force changes the initial wetting angle of the LM drop with surrounding surfaces and creates a movement of the original LM boundaries. The effect by which an electrostatic force creates a change in the wetting angle when the liquid metal is over a dielectric layer is called electro-wetting-on-dielectrics (EWOD). When the applied voltage is reduced the electrostatic force is also reduced and the liquid metal returns to its initial wetting angle due to its inherent surface tension/energies and disconnects the RF transmission line. Note that the change in the shape and dimensions of the LM drop may be of any form and direction, including moving of the center of the mass of the drop and stretching of the drop.
Alternatively, an electrostatic force can be applied between the drop and an electrode spaced apart (for example a via). This will cause the drop to move as a result not of EWOD but of direct electrostatic force action.
Advantageously, in microelectronics devices using LM drops disclosed herein, the operation of the LM drop by EWOD may be effected from all directions (top, bottom and sides). This is enabled by the use of regular metallic layers from top and bottom and uses of vertical electrodes (e.g. vias) from the sides. This is in contrast with known art, in which a LM contact can be operated from only two directions. Note that option does not exist in MEMS, which normally does not include a layered CMOS structure.
FIG. 2A shows in cross section an embodiment of a device 200 for RF switching using a LM drop in an open state. FIG. 2B shows device 200 in a closed state. Device 200 is similar to device 100 except that a RF transmission line 224 (which parallels 124 in FIG. 1A) serves also as one of the DC electrodes (electrode 224) and thereby simplifies the design. Electrode 224 is in constant contact with the drop.
FIG. 3A is a cross sectional view of an embodiment of a device 300 for DC or AC switching using a LM drop in an open state. FIG. 3B is a top view through section A-A of device 300. FIG. 3C shows device 300 in a closed state. Device 300 is similar to device 100 except that in the A-A section there are no ground lines, only DC lines 318 and 324, since the device is not used for RF purposes.
FIGS. 4A and 4B show in cross section an embodiment of a device 400 including a LM drop and used as a variable capacitor for RF switching or tuning (including in the THz region). FIG. 4A shows the device in a first state and FIG. 4B shows the device in a second state. Device 400 is similar to device 100 except that one of the RF ports (422) is covered with a dielectric insulating layer 448. Therefore, when the LM drop moves on layer 448 under an applied voltage, it changes the serial capacitance between RF transmission lines 418 and 424. As a voltage applied between DC conduction lines 430 and 436 is increased, the drop flattens and the RF serial capacitance is increased.
FIG. 5A shows in cross section yet another embodiment of a device 500 for RF switching using a LM drop in an open state. FIG. 5B shows device 500 in a closed state. Similar to device 100, device 500 includes a LM drop 502 inside a sealed cavity 504, the cavity located at least partially inside (and bound by) CMOS metallic layers 506 a-d, CMOS dielectric layers 508 a-d, 516 and 510. Device 500 further includes a first RF transmission (“signal”) line 518 extending between an end 520 and a first contact point 522 and a second RF transmission (“signal”) line 524 extending between an end 526 and a second contact point 528.
Device 100 also includes a first conduction line 530 which extends between a first end 532 and a second end 534, a second conduction line 536 which extends between a first end 538 and a second end 540, and a third conduction line 572 which extends between a first end 570 and a second end 574. In an embodiment, the conduction lines are connected to a direct current (DC) source. In another embodiment, the conduction lines are connected to an alternating current (AC) source. LM drop 102 is in permanent electrical contact with second end 540 and is electrically isolated from conduction lines 530 and 572 by dielectric layer 510 and other dielectric layers.
In use, in the “open” state, FIG. 5A, LM drop 502 has a left “front” 544 which does not contact points 522 of first RF electrode 518 and 528 of second RF electrode 524. Therefore, RF transmission cannot be performed by the device. As in the operation of other devices above, an electrostatic force can be applied on the LM drop through a designated voltage applied between the two DC electrodes. Due to EWOD, the drop changes its shape, FIG. 5B such that its left front 544 contacts the first and second contact point 522 and 528 respectively, therefore closing the transmission line and enabling the transmission of the RF signal through the switch “closed” condition. When the DC voltage is turned off on removed from DC line 530 and turned on applied to DC line 572, the LM drop is pulled back to the right side of the switch therefore disconnecting the first and second contact point 522 and 528 back to the “open” state.
To emphasize, in contrast with the use of device 100, in which when the DC voltage is turned to OFF the LM drop returns to its original shape due to its surface tension, in device 500 the switch is disconnected by applying a voltage on a different (added) electrode (572) and pulls the drop in order to disconnect it from the two RF ports currently drawn on the same side.
FIG. 6 shows schematically in top view through an appropriate section an embodiment of a 1×N switch 600 which includes a plurality N of switches 602 as in any embodiment in FIGS. 1-5, each switch positioned on a respective branch 604. This type of switch may be used for different purposes: (a) band selection by switching between different channels (either transmit channels of receive channels); (b) antenna selections when multiple antenna are used; (c) to frequency tune devices such as Power Amplifiers, Low Noise Amplifiers, filters, duplexes, multiplexes, resonators, oscillators, and essentially all type of devices in the radio front end. The latter may be done by loading the devices or impedance matching the devices using a bank of switched capacitors or inductors or both.
The N switches may be identical or different. Switch 600 includes a single input/output RF port 606 and N input/output RF ports 608-1 to 608-N. Each switch may be in an “open” or “closed” RF transmission state. Switch 600 may be used for selecting between transmission lines, to control a capacitance level, to control an inductance level or to control an impedance termination level.
In use for selecting between branches (of any kind), switch 600 will have usually one switch 602 in a closed state and all the other switches 602 is open state. When used for controlling a capacitance level or induction level or both, switch 600 will usually have one or more switches 602 in closed state and all the other switches 602 in open state. In an embodiment in which switches 602 are implemented using devices 400, the RF signals in RF ports 606-1 to 606-N will depend on the capacitance value of these devices which is controlled by the DC voltage applied on these devices as described above. When used for controlling an impedance termination level, the switch will be either in open state or, when in closed state, will reflect to the circuit an impedance level between Mega-ohms and zero ohm (grounded).
While this disclosure describes a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of such embodiments may be made. The disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.

Claims

1. A switching device comprising a liquid metal (LM) drop sealed in a cavity formed fully inside a microelectronic layered structure, wherein the LM drop is operable to obtain two switching states.

2. (canceled)

3. The device of claim 1, wherein the microelectronics layered structure includes CMOS layers and wherein the cavity has bottom and side walls bound by the CMOS layers.

4. The device of claim 1, further comprising at least two electrodes used to operate the LM drop to obtain the two switching states.

5. The device of claim 4, wherein at least one of the electrodes is a RF electrode.

6. The device of claim 4, wherein at least one of the electrodes is a non-RF electrode.

7. The device of claim 6, wherein the non-RF electrode is a DC or an AC electrode.

8. (canceled)

9. The device of claim 1, wherein the cavity is sealed by a sealing layer formed in a microelectronics process.

10. (canceled)

11. The device of claim 1, wherein the LM drop has a volume smaller than about 100 cubic micrometers.

12. The device of claim 1, wherein the LM drop has a volume between about 100 and about 10,000 cubic micrometers.

13. The device of claim 1, wherein the LM drop has a volume between about 10,000 and about 1,000,000 cubic micrometers.

14. The device of claim 1, wherein the LM drop has a volume between about 1,000,000 and about 10,000,000 cubic micrometers.

15. The device of claim 1, wherein the LM drop includes a gallium-indium-tin alloy.

16. The device of claim 1, wherein the cavity walls are treated with a wetting agent.

17. The device of claim 5, wherein the cavity has a bottom wall and further comprising a capacitor structure formed by a metal layer parallel to the cavity bottom wall and separated by a dielectric layer from the RF electrode.

18. The device of claim 3, further comprising at least two electrodes used to operate the LM drop to obtain the two switching states.

19. The device of claim 18, wherein at least one of the electrodes is a RF electrode.

20. The device of claim 18, wherein at least one of the electrodes is a non-RF electrode.

21. The device of claim 20, wherein the non-RF electrode is a DC or an AC electrode.

22. (canceled)

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. The device of claim 3, wherein the LM drop has a volume between about 100 and about 10,000 cubic micrometers.

28. The device of claim 3, wherein the LM drop has a volume between about 10,000 and about 1,000,000 cubic micrometers.

29. (canceled)

30. The device of claim 3, wherein the LM drop includes a gallium-indium-tin alloy.

31. The device of claim 3, wherein the cavity walls are treated with a wetting agent.

32. The device of claim 19, wherein the cavity has a bottom wall and further comprising a capacitor structure formed by a CMOS metal layer parallel to the cavity bottom wall and separated by a dielectric layer from the RF electrode.

33. The device of claim 3, wherein the CMOS layers have a total thickness less than about 10 micrometers.

34. The device of claim 3, wherein the cavity is sealed by a CMOS dielectric layer.

35. The device of claim 1, wherein the microelectronics layered structure includes MEMS layers and wherein the cavity has bottom and side walls bound by the MEMS layers.

36. The device of claim 1, wherein the microelectronics layered structure includes interposer layers for multiple IC integration and wherein the cavity has bottom and side walls bound by the interposer layers.

37. The device of claim 36, further comprising at least two electrodes used to operate the LM drop to obtain the two switching states.

38. The device of claim 36, wherein the LM drop has a volume between about 100 cubic micrometers and about 1,000,000 cubic micrometers.

39. The device of claim 36, wherein the LM drop includes a gallium-indium-tin alloy.

40. The device of claim 36 wherein the cavity walls are treated with a wetting agent.

41. A switching device comprising a liquid metal (LM) drop having a height on the order of the total thickness of interposer layers for multiple IC integration, and wherein the LM drop is operable to obtain two switching states.

42. The device of claim 41, wherein the LM drop has a volume between about 100 cubic micrometers and about 1,000,000 cubic micrometers.

43. The device of claim 41, further comprising at least two electrodes used to operate the LM drop to obtain the two switching states.

44. The device of claim 43, wherein at least one of the electrodes is a RF electrode.

45. The device of claim 43, wherein at least one of the electrodes is a non-RF electrode.

46. The device of claim 45, wherein the non-RF electrode is a DC or an AC electrode.

47. The device of claim 41, wherein the LM drop includes a gallium-indium-tin alloy.

48. The device of claim 41 wherein the cavity walls are treated with a wetting agent.

49. The device of claim 45, wherein the cavity has a bottom wall and further comprising a capacitor structure formed by a metal layer parallel to the cavity bottom wall and separated by a dielectric layer from the RF electrode.