The invention relates generally to semiconductor structures and devices and, more particularly, to structures, devices, and integrated circuits utilizing liquid logic and methods of fabricating such structures, devices, and integrated circuits.
Semiconductor devices, such as field effect transistors (FET's), are familiar building blocks of integrated circuits formed in silicon substrates. A single silicon-based integrated circuit may feature many thousands to millions of FET's, along with other passive components such as resistors and capacitors. However, silicon based technologies face certain limitations. Limitations on silicon wafer size limit use in large area electronics. The high temperature processing required during silicon device processing prevents the use of low-cost substrates, such as plastics, and limits the application of advanced fabrication technologies, such as roll-to-roll processing. Silicon-based electronics are difficult to integrate seamlessly with chemical/biological components. A full extension to three-dimensional device structures is unlikely with silicon-based technologies. Silicon device structures are fundamentally planar and are therefore difficult, if not impossible, to adapt to non-planar surfaces.
Various nontraditional alternatives have been proposed to conventional silicon technologies. One alternative, quantum computing, has limited applications and has encountered manufacturing difficulties. Another alternative, DNA computing, is time consuming and suffers from imprecise operation. Yet another alternative, microfluidic computing, has found only limited applications. Still another alternative, organic electronics, offers limited performance, lifetime and reliability.
What is needed, therefore, is a switching scheme for device fabrication that does not suffer from the limitations of conventional silicon-based device technologies and the limitations of proposed alternatives to silicon-based device technologies.
The invention is directed to electronics based on electrically-controlled liquid components. More specifically, the invention is directed to the operation of individual electronic components (e.g., diodes, latches, transistors), wherein the active medium is composed of one or more liquids, to integrated electronic circuits incorporating components containing liquids and to systems that utilize such circuits.
In accordance with the principles of the invention, structures, devices and integrated circuits are provided with liquid logic. Liquid logic enables the fabrication of large area electronics (i.e., electronics on the human scale) such as flat panel displays, large array antennas, scanners/printers/copiers, large area sensors operating by chem/bio principles, thermal sensing, and radiation detection, full-size medical imaging systems, and photovoltaics. The liquid logic of the invention may be fabricated at room temperature, which permits the implementation of plastic substrates which are flexible and inexpensive and permits roll-to-roll processing. The liquid logic of the invention provides higher functionality by permitting the integration of various technologies/devices (i.e., hybrid electronics). The liquid logic of the invention increases packing density, which may permit fabrication of multi-layer or three-dimensional circuits of higher density than currently possible with conventional device technologies. The liquid logic of the invention is applicable to non-planar surfaces, unlike silicon-based technologies. For example, sensors may be formed using the liquid logic of the invention on curved surfaces of aircraft and spacecraft, soldiers, and other large-scale structures such as vehicles, power plants, bridges, etc. The liquid logic of the invention may also be applied to fabricate flexible electronics, such as electrotextiles (i.e., wearable electronics), electronic newspapers, and flexible large area displays and signs. The liquid logic devices of the invention utilize electric-field-controlled liquid components, which are distinguishable over devices in which liquid components are mechanically controlled, such as mercury switches.
The liquid logic devices of the invention are expected to exhibit superior electrical properties as compared with conventional alterative to silicon device technologies. Both n-channel and p-channel devices may be formed, which permits the creation of CMOS-like circuits that operate at low power. The carrier mobility is higher in the liquid logic devices of the invention than available in Organic FET's or amorphous silicon. The inventive liquid logic devices have a high current capability and are capable of bistable operation at low power. The inventive liquid logic devices are versatile in that CMOS-like transistors may be applied to many diverse applications. The inventive liquid logic devices may be formed by simple, room temperature fabrication techniques at a very low cost and using plastic substrates. The inventive liquid logic devices may be fabricated by non-lithographic wet/soft processing methods, such as ink jet printing, molding, and stamping, and may be formed by roll-to-roll fabrication techniques. The inventive liquid logic may be easily integrated with micro- and macro-fluidic applications.
The liquid logic and electrowetting switching of the invention may be applied to fabricate various device types, including but not limited to latches, transistors and inverters. Transistors may be formed with either upright or inverted component arrangements and as either p-channel or n-channel devices, which are easily and conveniently integrated on a single substrate.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
In accordance with the various embodiments of the invention, electric fields are used in a device structure to manipulate the position and/or geometrical shape of one or more fluids or liquids using electrowetting for controlling the flow of current between electrodes of the device structure. Generally, one of the liquids is conductive and a second liquid, if present, is electrically insulating or also electrically conducting, certain surfaces of the device structure are either hydrophilic or hydrophobic, and the physical space occupied by one or more of the liquids can be manipulated by the application of an electric field. Electrowetting permits the fundamental switching process to be implemented using liquids. In terms of the external connections with the liquid-based device, voltages and currents very similar to conventional silicon-based CMOS devices are expected to be required, although the invention is not so limited.
With reference to FIGS. 1A,B and 2A,B and in accordance with one embodiment of the present invention, a transistor having a single gate latch, generally indicated by reference numeral 10, is actuated using electrowetting-induced actuation for energizing or switching the operation of a functional device 12, such as a light-emitting diode (LED). The transistor 10 is fabricated on a substrate 14 and may be among multiple identical transistors 10 fabricated on substrate 14. The transistor 10 includes a source region 16, a drain region 20 spaced from the source region 16 by an electrically-insulating gap or non-conducting channel 15, a gate electrode 22, and an electrolyte droplet 24 positioned for selectively bridging the gap 15 to create current flow from the source region 16 to the drain region 20. The drain region 20 is coupled electrically with a power supply 18 and the gate electrode 22 is coupled electrically with a power supply 25. The electrolyte droplet 24 is constantly shorted to the drain region 20, which is held at a drain voltage of, for example, about five (5) volts. Therefore, the electric potential of the droplet 24 is approximately equal to the drain voltage of the drain region 20 regardless of whether the transistor 10 is in an on (i.e., conducting) state or an off (i.e., non-conducting) state.
Although not shown in FIGS. 1A,B, all or a portion of the exposed surface of gate electrode 22, which is typically formed from a metal or other highly conductive material, is coated by a layer of an electrical insulator 26 (FIGS. 2A,B). The extent to which the electrical insulator 26 covers the gate electrode 22 is sufficient to electrically insulate the constituent conductive material from the electrolyte droplet 24 as the droplet 24 changes shape and/or position, as appropriate. The electrical insulator 26 covering the gate electrode 22 should be hydrophobic to furnish a relatively large liquid/solid contact angle. Optionally, a hydrophobic coating 28 (FIGS. 2A,B), such as DuPont TEFLON®, Asahi CYTOP®, or Cookson Parylene, may be applied to the surface of the electrical insulator 26 contacting the electrolyte droplet 24 in order to provide the necessary hydrophobicity.
The hydrophobicity of the surfaces of the source region 16 and drain region 20 wetted by the electrolyte droplet 24 permits the droplet 24 to freely make or release contact therewith, as regulated by voltage supplied from gate electrode 22. Exemplary hydrophobic materials include, but are not limited to, covalently bonded (i.e., non-polar) semiconductors such as Si, Ge, SiGe, and SiC. Conductive carbon films may also supply the desired hydrophobicity and electrical conductivity. Furthermore, the source and drain regions 16, 20 may be formed from a metal and coated at least across surface portions wetted by the droplet 24 with a very thin (about 10 mn or less) film of a hydrophobic fluoropolymer, such as TEFLON® commercially available from E. I. duPont deNemours and Company of Wilmington, Del. Fluoropolymer layers of this thickness are believed to exhibit adequate electrical conductivity due to electron tunneling to provide a current path to the underlying material of the source and drain regions 16, 20, while maintaining a high degree of hydrophobicity. In addition, thin or thick hydrophobic films may be used in conjunction with electrical conductor, semiconductor, or insulator films to create composite films that are hydrophobic and insulating, semiconducting, or electrically conducting.
The substrate 14 may be any material having a surface suitable for fabricating the source region 16, drain region 20 and gate electrode 22 and onto which the droplet 24 may be deposited. The characteristics of this surface of substrate 14 are also suitable to permit the droplet 24 to be moved and/or experience a change in contact angle upon the application of an electric field from gate electrode 22. Exemplary materials for substrate 14 include any flexible or rigid polymer recognized as suitable for use in the invention by a person of ordinary skill in the art. The substrate 14, or additional materials placed on the substrate 14, may be embossed, stamped, micro-replicated, or contain wells or channels or other non-planar features which assist in isolation, motion control, and containment, of various liquids of the present invention.
The material constituting the substrate 14 may have a high enough resistivity such that, if the source and drain regions 16, 20 are not bridged by droplet 24, there is no current path across the channel 15 through which significant electrical current could flow between the source and drain regions 16, 20. Accordingly, the channel 15 is non-conducting in this state.
The electrolyte constituting droplet 24 may be any suitable conductive fluid, including but not limited to an aqueous solution of an ionic compound, such as potassium chloride dissolved in water. The electrolyte may optionally include non-electrolytic liquids, like Acetonitrile. The droplet 24 may be formed from a liquid metal, such as mercury (Hg) or gallium (Ga) or a metal alloy like an indium/gallium (In/Ga) alloy. The droplet 24 may also be a liquid conducting molecule like methanol, an inorganic/organic mixture like polyethylenethioxythiophene (PEDOT) mixed with water, or a mixture of a dielectric fluid with a conducting fluid, such as a mixture of water with one of the Fluorinert™ electronic liquids commercially available from 3M Corporation of St. Paul, Minn. The electrolyte droplet 24 may consist of multiple individual sub-droplets of conducting fluids that collectively form droplet 24.
The electrolyte droplet 24 has a characteristic contact angle with the surface of substrate 14. The contact angle represents the angle formed as a result of contact between the droplet 24 and substrate 14, and reflects the interfacial affinity between the droplet 24 and substrate 14 (i.e., the wettability of the substrate with respect to the droplet). The contact angle is inversely related to interfacial affinity. For example, a highly hydrophilic substrate 14 forms a low contact angle with respect to droplet 24. Similarly, a highly hydrophobic substrate 14 forms a high contact angle with respect to droplet 24.
In use and with continued reference to FIGS. 1A,B and 2A,B, a voltage applied to the electrolyte droplet 24 causes droplet 24 to wet (i.e., contact angle decrease as shown in
As a result of the increased wetting of gate electrode 22, the electrolyte droplet 24, which is continuously shorted to the drain region 20, changes shape so as to contact the surface of source region 16 and, as a result, is then also shorted to the source region 16. The ensuing bridging of the non-conducting channel 15 between the source region 16 and drain region 20 by droplet 24 permits current to flow through the droplet 24 from source region 16 to the drain region 20, which places the transistor 10 in the on state. Portions of the droplet 24 thereby define a current path between the source and drain regions 16, 20. Current then flows from the drain region 20 to the functional device 12, which energizes device 12.
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The source and drain electrodes 56, 58 are hydrophobic or coated with an electrically conductive hydrophobic layer 64. The drain 58 is electrically coupled with the power supply 66. A portion of the substrate 53 operates as a second electrode 57 that is electrically isolated from the electrolyte 60 by an insulating layer 55, and the insulating layer 55 may be covered by an optional hydrophobic layer 61 if the insulating layer 55 is not sufficiently hydrophobic.
The surface tension (about 20-30 dynes/cm) of the oil film 54 is significantly lower than the surface tension (about 40-70 dynes/cm) of the electrolyte 60. This forces the oil to prefer to form a film 54 between the electrolyte 60 and the hydrophobic source and drain electrodes 56, 58 (about 15-20 dynes/cm). The oil film 54 (
In use, the transistor 50 is initially in an off state as shown in
The construction of the transistor 10 (FIGS. 1A,B), transistor 30 (FIGS. 2A,B), and transistor 50 (
Voltage-complimentary liquid transistors may be integrated to create liquid integrated circuits performing common Boolean functions such as AND, OR, and NOR, or forming inverters, buffers, or any circuit or collections of circuits. Single liquid transistors (three or more electrodes), or even simple liquid diodes (two electrodes), of the present invention may be utilized for computing, switching, amplifying, sensing, or other electronic, opto-electronic, biomedical, micro-mechanical, sensor, transmission, or receiving applications.
In accordance with an alternative embodiment of the invention, any of the transistor 10 (FIGS. 1A,B), transistor 30 (FIGS. 2A,B), and transistor 50 (
The following example illustrates particular properties and advantages of some of the embodiments.
The prototype liquid logic device described in the example is most consistent with the device operation outlined in FIGS. 1A,B. A 3″ Si wafer was coated with an electrically insulating and hydrophobic DuPont Teflon AF fluoropolymer coating. An electrically conductive droplet containing water and PEDOT/PSS aqueous conductive polymer was then placed on the wafer. A drain electrode was inserted into the droplet, and a source electrode was placed adjacent to the droplet. The source and drain electrodes were then attached to an external battery and a functional device (LED) circuit. A gate electrode was attached to the upper surface of the droplet and a variable voltage source attached to the droplet with reference to the wafer (which acted as ground).
Upon application of an appropriate gate voltage (10V to 40V) to the droplet, the droplet wetted the hydrophobic surface of the wafer. This decreased the contact angle of the droplet to the hydrophobic surface and caused the droplet to contact the source electrode. This further caused the drain and source electrodes to short together, which enabled current flow in the functional circuit and caused the LED to turn on. The measured current in the functional circuit in the off state was zero (0) mA, and in the on state was five (5) mA. The gate electrode passed no measurable DC current into the system because the gate electrode was electrically insulated from the wafer, which was held at ground. Removing the gate voltage had the effect of allowing the droplet to return to its original state (de-wet the hydrophobic surface) and remove itself from contact with the source electrode. This turned the system “off” and darkened the LED.
While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants' general inventive concept.
This application claims the benefit of U.S. Provisional Application No. 60/573,662, filed on May 21, 2004, the disclosure of which is hereby incorporated by reference herein in its entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2005/017752 | 5/20/2005 | WO | 00 | 11/20/2006 |
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WO2005/114740 | 12/1/2005 | WO | A |
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