The present disclosure is directed generally to nanoelectromechanical systems (NEMS) devices with metal-to-metal contacts.
Nanotechnology provides techniques or processes for fabricating structures, devices, and systems with features at a molecular or atomic scale, e.g., structures in a range of one to hundreds of nanometers in some applications. For example, nano-scale devices can be configured to sizes similar to some large molecules, e.g., biomolecules such as enzymes. Nano- sized materials used to create a nanostructure, nanodevice, or a nanosystem that can exhibit various unique properties including optical properties, that are not present in the same materials at larger dimensions and such unique properties can be exploited for a wide range of applications.
Techniques, systems, and devices are described related to nanoelectromechanical systems (NEMS) devices and for implementing and fabricating nanoelectromechanical systems (NEMS) devices with conducting contacts.
The subject matter described in this disclosure can be implemented in specific ways that provide one or more of the following features. For example, the disclosed NEMS switches exhibit no or minimal leakage current in the OFF state, offer low insertion loss, include air gaps providing high isolation, and can be fabricated at a low cost.
According to an aspect is a nanoelectromechanical system (NEMS) switch. The switch includes: (i) a substrate; (ii) a source cantilever formed over the substrate and configured to move relative to the substrate; (iii) a drain electrode and at least one gate electrode formed over the substrate, wherein the source cantilever, the drain, and the at least one gate electrode comprises a metal layer affixed to a support layer, at least a portion of the metal layer at a contact area between the metal layer and support layer extending past the support layer; and (iv) an interlayer sandwiched between the support layer and the substrate.
According to an embodiment, each of the source cantilever, the drain, and the at least one gate electrode are separated by air gaps.
According to an embodiment, the metal comprises platinum, gold, tungsten, or nickel.
According to an embodiment, the support layer comprises silicon, silicon dioxide, or silicon nitride.
According to an embodiment, the source cantilever is configured to deflect laterally with respect to the substrate.
According to an embodiment, the interlayer is an insulator. According to an embodiment, the insulator comprises silicon, silicon dioxide, or silicon nitride.
According to an aspect is a method for manufacturing a NEMS switch comprising a metal overhang at the source cantilever, the drain, and the at least one gate electrode. The method includes etching a portion of the support layer at a contact area.
According to an embodiment, the step of etching the support layer comprises a gaseous phase dry isotropic etch. According to an embodiment, the step of etching the support layer comprises a liquid phase wet isotropic etch. According to an embodiment, the step of etching the support layer comprises a focused ion beam configured to remove a portion of the support layer at the contact area.
According to an aspect is a nanoelectromechanical system (NEMS) switch. The switch includes: (i) a substrate; (ii) a source cantilever formed over the substrate and configured to move relative to the substrate; (iii) a drain electrode and at least one gate electrode formed over the substrate, wherein the source cantilever, the drain, and the at least one gate electrode comprises a metal layer; and (iv) an interlayer sandwiched between the metal layer and the substrate.
According to an embodiment, the metal layer comprises molybdenum silicide, platinum, gold, tungsten, or nickel.
According to an embodiment, the interlayer is an insulator. According to an embodiment, the insulator comprises silicon, silicon dioxide, or silicon nitride.
According to an aspect is a method for operating a NEMS switch. The method includes: (i) applying voltage potentials to a first gate electrode; (ii) determining the first gate electrode's voltage that causes a source cantilever of the NEMS switch to contact a drain electrode of the NEMS switch; (iii) pre-biasing the NEMS switch by applying a voltage to the first gate whereby the pre-biased voltage is less than the gate voltage required to bring the source cantilever in contact with the drain electrode; (iv) applying a voltage on a second gate electrode to bring the source cantilever into contact with the drain electrode; and (v) transferring a signal between the source cantilever and the drain electrode.
According to an embodiment, the source cantilever, the drain electrode, and the first gate electrode comprise a metal layer affixed to a support layer, at least a portion of the metal layer at a contact area between the metal layer and support layer extending past the support layer.
According to an embodiment, the NEMS switch further comprises an interlayer sandwiched between the support layer and the substrate.
Techniques, systems, and devices are described in detail herein and below related to nanoelectromechanical systems (NEMS) devices and for implementing and fabricating nanoelectromechanical systems (NEMS) devices with conductive contacts. In one aspect, a NEMS device can include a substrate, a source cantilever formed over the substrate and configured to move relative to the substrate, a drain formed over the substrate, and first, second and third gates formed over the substrate and separated from the source by first, second and third gaps, respectively. The source cantilever, the drain, the first, second and third gates form a NEMS actuator switch in which the source cantilever moves relative to the substrate in response to control voltages applied to the source cantilever, the drain, and the first, second and third gates. In some implementations of the device, for example, the device can be pre-biased at an electrical signal substantially close to a gate contact voltage. In some implementations of the device, for example, the substrate can include Si, Ge, SiC, pyrex and glass.
The source cantilever, the drain, and the first, second and third gates can include a metal or a metal affixed to a support structure. In some implementations of the device, for example, the third gate can be electrically floating, the drain can be set at an electrical potential, and the source cantilever can be configured to switch between different positions in response to varying control voltages applied to the first and second gates. In some implementations of the device, for example, the device can further include a junction gate field effect transistor (JFET) formed over the substrate to include a JFET drain, a JFET source, and a JFET gate, in which the JFET gate is coupled to the source cantilever to form a JEFT-NEMS actuator switch.
In one embodiment, for example, an exemplary NEMS-based actuator device can include a NEMS switch design in which the air gaps are configured to be larger such that there is no pull-in during the operation of the switch. For example, a metal can be used as the structural and conducting contact material for the NEMS switch in this exemplary design.
To reduce gate leakage current and polydepletion effects in future generations of advanced transistors such as the FinFET or Ultrathin-Body MOSFET, the International Roadmap for Semiconductors (ITRS) has suggested the use of high-k gate dielectrics and dual-metal-gate electrodes. The inventor has recognized that molybdenum silicide (MoSix) and pure Molybdenum (Mo) seem to be the ideal metal gate stack because of the appropriate workfunctions to n-channel and p-channel devices respectively. Hence, MoSi2 is a material in commercial foundries.
At the same time, MEMS technology is currently leveraging various materials such as silicon, silicon dioxide and MoSi2 layers that are present in CMOS technology. Besides MoSi2 being a great midgap metal for the next generation of transistors, it has a high Young's modulus (430 GPa) which makes it ideal as a structural material for nanostructures such as accelerometers, switches and gyroscopes. MoSi2 also exhibits a superb etch resistance to HF and Buffered Oxide Etch. Herein, described in an embodiment, is the use of MoSi2 as a structural material for a NEMS switch. NEMS switches are favored for their near zero ideal power dissipation and abrupt ON-OFF state transitions. But some of the major challenges in NEMS switches are stiction of the source terminal to the drain, high switching voltages, stress gradient in the structural material used and maintaining a low contact resistance. Disclosed is an exemplary NEMS switch that is CMOS compatible and addresses some of these challenges.
The disclosed NEMS switch is designed to operate in non-pull-in fashion. Pull-in is an instability phenomenon where, for example, in a parallel plate capacitor with the bottom plate fixed and the top plate free to move displaces one-third of the actuation gap and the electrical force becomes larger than the mechanical restoring force. Under this condition, the top plate becomes unstable and snaps or pulls-in to the bottom plate.
The pull-in voltage is given by the following equation:
where Vp represents the pull-in voltage, K is the spring constant of the cantilever, do is the initial actuation gap, ε is the permittivity of the dielectric in the actuation gap, in this case its air and A is the actuation area. Equation 1 stipulates that to prevent pull-in the actuation gap has to be increased.
The advantage of pre-biasing the device is that the switching voltage of the switch can be dramatically decreased to sub-1 V because the contact gap that needs to be closed is very small and as a result, small voltage on G2 causes switching. Pre-bias is similar to the back-bias used in CMOS for adjusting the transistor threshold voltage. For example, sub- 500 μV switching voltages demonstrated using the pre-bias scheme. Also, since the All-Metal structure is formed on an insulating layer (oxide layer), voltage transients applied to G1 feedthrough the buried oxide layer and air to G3 to generate a floating potential.
This automatic pull-back mechanism helps to mitigate the stiction problem which plagues NEMS switches.
The fabrication of the device is detailed in
Referring to
In
In
⅓MoSi2+O2=⅔SiO2+⅓MoO2 (2)
2MoO2+O2=2MoO3 (3)
The MoSi2 surface is believed to be covered with a duplex oxide layer of SiO2+MoO3. This duplex layer can easily absorb carbonaceous contaminants as well as water vapor and hydrocarbons.
When the switch was tested in a vacuum probe station, at low pressures of 0.1 mbars, there was not significant current flow from the drain to the source until the pressure reached ˜4e-4 mbars. At this pressure, the water vapor and the hydrocarbons desorbed from the contact area. To investigate the gate contact voltage, the source was grounded and 8 V applied to the drain. G2 and G3 were made to float and a 100 nA current compliance set for the drain and source currents. Voltage ramps were applied to Gi until the source contacted the drain. Both the source and drain currents were monitored.
With the gate contact voltage determined as 48.2V, the device was pre-biased to 45 V and voltage ramps applied to G2 to usher in full contact.
The drain voltage has an effect on the switching voltage. As the source-drain gap decreases, any additional drain voltage will generate excess electric field that will abruptly attract the source to the drain. This phenomenon is similar to the conventional pull-in effect in NEMS devices but here, the source cantilever does not have to be displaced one-third of the air gap before it experiences instability and initiate a pull-in effect.
To further investigate the possibility of the partial breakdown of the duplex layer, the switch was fully closed and the drain voltage ramped from 0 V to 8 V.
The reliability of the switch was examined in exemplary implementations by pre- biasing G1 at 45 V and 8 V applied to the drain with the source grounded. A 50% duty cycle AC signal was applied to G2 with a peak-to-peak voltage of 18 V, running at 10 KHz. The drain current was sampled every 2 seconds and the implementation terminated when the value of the drain current reduced 8 times. For example, 302,240 cycles where accrued. For example, dielectric charging of the duplex layer may have caused the source to be stuck to the drain in this exemplary implementation. The exemplary device utilized in this exemplary implementation was inspected using SEM, but showed that the source was separated from the drain. For example, it is possible that during the transfer of the switch to the SEM, the dielectric layer was fully discharged.
In one embodiment, the entire switch was fabricated from metal (i.e., gold) as shown in
In another embodiment, to control the amount of stress gradient in the source cantilever, the metal layer was affixed to a structural support layer as shown in
In addition, to ensure that a metal-to-metal contact is achieved between the source cantilever and the drain electrode, the portion of the support layer at the contact area could be removed either by dipping the device in a solution that etches the support layer or by using an isotropic dry etch to perform the undercut.
Referring to
In
In
In
In another embodiment, using the same process flow as illustrated in
The process described in
While various embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, embodiments may be practiced otherwise than as specifically described and claimed. Embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.
The above-described embodiments of the described subject matter can be implemented in any of numerous ways. For example, some embodiments may be implemented using hardware, software or a combination thereof. When any aspect of an embodiment is implemented at least in part in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single device or computer or distributed among multiple devices/computers.
Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.
This application is a Continuation Application of U.S. patent application Ser. No. 15/945,792, filed Apr. 5, 2018, which application claims priority to U.S. Provisional Patent Application Ser. No. 62/482,478, filed Apr. 6, 2017, entitled “Nanoelectromechanical Devices with Metal-to-Metal Contacts,” the entire disclosures of which are incorporated herein by reference in their entireties.
Number | Date | Country | |
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62482478 | Apr 2017 | US |
Number | Date | Country | |
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Parent | 15945792 | Apr 2018 | US |
Child | 16990599 | US |