Magnetic nanomechanical devices for stiction compensation

Nanoelectromechanical (NEMS) devices having nanomagnets for an improved range of operating voltages and improved control of dimensions of a cantilever are described. For example, in an embodiment, a nanoelectromechanical (NEMS) device includes a substrate layer, a first magnetic layer disposed above the substrate layer, a first dielectric layer disposed above the first magnetic layer, a second dielectric disposed above the first dielectric layer, and a cantilever disposed above the second dielectric layer. The cantilever bends from a first position to a second position towards the substrate layer when a voltage is applied to the cantilever.

TECHNICAL FIELD

Embodiments of the invention are in the field of magnetic devices and, in particular, nanoelectromechanical devices for stiction compensation.

BACKGROUND ART

A nanoelectromechanical (NEMS) relay operates like a switch. The NEMS relay uses a voltage to physically open and close a circuit. The NEMS relay has the advantage of energy efficiency by not leaking current when turned off unlike CMOS transistors. However, the physical dimensions at which the nanorelays are operational at low voltages are limited and manufacturing tolerances are small.

DETAILED DESCRIPTION

Nanoelectromechanical (NEMS) devices with nanomagnets for stiction compensation are described. In the following description, numerous specific details are set forth, such as specific magnetic layer integration and material regimes, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

One or more embodiments are directed to NEMS devices with nanomagnets for improved control of an operating voltage of the NEMS device (e.g., lower operating voltage of the NEMS device) and improved control of a size of a cantilever and control of a gap between the cantilever and a substrate of the NEMS device. Applications may include use in CPUs, processors, chipsets, wireless devices, etc. for computations (e.g., lower performance computations).

FIG. 1illustrates a cross-sectional view of a nanoelectromechanical (NEMS) device in accordance with a conventional approach. The device100includes a silicon substrate110that acts as a ground electrode, an oxide layer120, a SiO2 layer130, and polysilicon layer140and142. The layer140is a cantilever that includes a free end that moves towards the substrate if a voltage is applied to the layer140as illustrated inFIG. 1. The free end moves away from the substrate if no voltage is applied to the layer140(e.g., Vdd electrode).

FIGS. 2A and 2Billustrate cross-sectional views of a nanoelectromechanical (NEMS) device with nanomagnets, in accordance with an embodiment of the present invention. The device200includes a substrate layer210(e.g., a silicon substrate layer), a non-magnetic layer220disposed above the substrate layer, a first magnetic layer230disposed above the non-magnetic and substrate layers, a first dielectric layer240disposed above the first magnetic layer, a second dielectric250(e.g., sacrificial oxide) disposed above the first dielectric layer, and a cantilever280. The cantilever280includes a magnetic layer262and a polysilicon layer272. The magnetic layer260may be formed from the same or different magnetic layer in comparison to magnetic layer262. The polysilicon layer270may be formed from the same or different polysilicon layer in comparison to polysilicon layer272.FIG. 2Aillustrates the cantilever280in a first position with no voltage applied between the polysilicon layer272(i.e., Vdd electrode) and the substrate210(i.e., ground electrode).FIG. 2Billustrates the cantilever280in a second position with voltage (e.g., Vdd) applied between the polysilicon layer272(i.e., Vdd electrode) and the substrate210(i.e., ground electrode) for a certain time period (e.g., 1 nanosecond). The cantilever bends from a first position to a second position in contact with the first dielectric layer when a voltage is applied to the cantilever. The cantilever is restored from the second position to the first position having no contact with the first dielectric layer when the voltage is removed from the cantilever. The substrate layer210acts as a ground electrode when the voltage (Vdd) is applied to the cantilever. The cantilever has a length282, a thickness284, and a gap286represents a distance from a lower surface of the cantilever to an upper surface of the dielectric layer240.

In one embodiment, the non-magnetic layer includes at least one of Ruthium (Ru), Tantalum (Ta), Titanium (Ti), Zirconium (Zr), Hafnium (Hf), and Magnesium (Mg). The non-magnetic layer provides a crystallization template (e.g., orientation) for the magnetic layer230. The magnetic layers230,260, and262may include Cobalt (Co) or other suitable ferromagnetic layers (e.g., Fe). The dielectric layer240may be magnesium oxide (MgO) or any other appropriate dielectric layer.

The magnetic layers230and262(e.g., nanomagnets) remain magnetized in the same direction because of their size (e.g., long and thin) and magnetic anisotropy. These nanomagnets produce magnetic repulsion force that counteracts an adhesion force of the cantilever and improves the range of operational voltages and size ranges for the cantilever as discussed below.

FIG. 3illustrates a plot of cantilever length versus cantilever thickness for different gaps in accordance with one embodiment of the present invention. The plot300shows cantilever length (nanometers (nm)) versus cantilever thickness (nm) for a silicon cantilever operating at 1 volt (i.e., Vdd of 1 volt) for gaps of 2, 3, 4, and 5 nm between a lower surface of a cantilever and an upper surface of the substrate. This particular device, which does not include nanomagnets, does not work in the dimension of interest at gap separations of 5 nm or greater, hence the absence of 5 nm shaded regions in the plot. Gaps of less than 2 nm have not been shown on the plot because tunneling current begins to be significant in this regime. For the non-operational region below the 2 nm region, the cantilever is stiff (e.g., not able to bend sufficiently) due to a short length and does not have a sufficient electrostatic force from the applied voltage. For the non-operational region above the 4 nm region, the cantilever is soft (e.g., remains in a bent position in contact with a dielectric layer) due to a longer length and does not have a sufficient electrostatic force from the applied voltage to overcome the adhesion force. The optimistic adhesion force used for the plot includes only van der Waals forces. Environmental conditions such as humidity and metallic bonding can increase stiction by as much as two order of magnitude have not been accounted for in this plot. Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. These environmental conditions are undesirable and would modify the operational range, but not the general trends in the plot300.

When nanomagnets are included in the design of the device, then the operational range is increased as illustrated inFIG. 4.FIG. 4illustrates a plot of cantilever length versus cantilever thickness for different gaps in a device that includes nanomagnets in accordance with one embodiment of the present invention. The plot400shows cantilever length (nanometers (nm)) versus cantilever thickness (nm) for a silicon cantilever operating at 1 volt (i.e., Vdd of 1 volt) for gaps of 2, 3, 4, and 5 nm between a lower surface of a cantilever and an upper surface of the substrate. This particular device, which does include nanomagnets, does not work in the dimension of interest at gap separations of 5 nm or greater, hence the absence of 5 nm shaded regions in the plot. Gaps of less than 2 nm have not been shown on the plot because tunneling current begins to be significant in this regime. The optimistic adhesion force used for the plot includes only van der Waals forces.

The plots300and400have been simulated using a parallel plate relay. The restoring force originates from the effective spring constant of the cantilever while the electrostatic force originates from the analytical electrostatic attraction between parallel plates. The adhesion forces were calculated with density functional theory expanded with a force field that accounts for van der Waals interactions. The magnetic forces were calculated using a model to scale the forces from atomic dipole-dipole interactions into the continuum regime. To verify that the parallel plate relay model is reliable, the spring restoring force of a silicon cantilever as a function of the actuation voltage was calculated numerically accounting for fringing capacitance and different cantilever geometries with the results being plotted inFIG. 5Afor a cantilever in accordance with one embodiment of the invention. The cantilever has a width of 5 nm, a gap that varies from 3-30 nm, a thickness that varies from 3-30 nm, and a length that varies from 100-300 nm in length. The data points with a higher restoring force have a higher cantilever thickness while the data points with a lower restoring force have a smaller gap.

The nanomagnets improve the robustness of this device by expanding the gap operational range since the gap is the smallest and most difficult dimension to control and the device is very sensitive to this parameter. The nanomagnets also allow an overlap of the operational regions at different thicknesses (e.g., 2-4 nm) as illustrated in the plot400. For example, the region410is an overlap region where the device is operational for gaps of 2, 3, and 4 nm. For this overlap region410, the device has a length of approximately 250-300 nm and a thickness of approximately 25-30 nm. In this embodiment, the magnetic material occupies approximately half of the cantilever although other dimensions for the magnetic material will work as well. A strong nanomagnet includes a magnetic moment similar to iron and the operational range can be further optimized by selected an appropriate magnetic element or alloy.

FIG. 5Billustrates a plot of cantilever thickness at a minimum voltage (e.g., 1 volt) versus cantilever length for a device that includes nanomagnets and for a device that does not include nanomagnets in accordance with one embodiment of the present invention. The plot550shows cantilever thickness (nanometers (nm)) versus cantilever length (nm) for a silicon cantilever operating at 1 volt (i.e., Vdd of 1 volt) for a device with no magnets and for a device with nanomagnets. When the cantilever is longer than about 100 nm, the nanomagnets reduce the thickness necessary to operate the cantilever. The thickness and length of the cantilever determine a restoring force needed to restore the cantilever from a bent position as illustrated inFIG. 2Bto a restored position as illustrated inFIG. 2A.

NEMS devices (e.g., NEMS relays or switches) can be made by techniques currently used to fabricate CMOS chips and have recently been used for computation applications. The NEMS devices are currently at least 100 times slower than CMOS devices, but have no leakage current. A NEMS device capable of computation can be achieved in several ways. For example, the NEMS relay that has been modeled and plotted includes a silicon cantilever and substrate. When a voltage is applied, an electrostatic force bends the cantilever towards the substrate. An operational cantilever makes contact during the time that the voltage is applied as illustrated inFIG. 2Band returns to its original position as illustrated inFIG. 2Aafter the voltage is removed due to its restoring force. A first failure mode is the cantilever being so stiff that it does not make contact while a second failure mode is the cantilever being so soft that it can not separate from the dielectric layer disposed on the substrate due to van der Waals forces or other adhesion forces. Therefore, for the device to work, the electrostatic force has to be greater than a restoring force and the restoring force greater than an adhesion force as illustrated inFIG. 6-8.

FIG. 6illustrates a NEMS device for switching from a first position (e.g., logic level 0) to a second position (e.g., logic level 1). The device600includes a source region610that includes a cantilever612, a drain region620, and a gate region630. Application of an electrostatic force640causes the cantilever612to bend towards the drain region620with a free end of the cantilever contacting the drain region620if the electrostatic force and adhesion force642are greater than a spring restoring force644. The device switches from the first position650(e.g., logic level 0) to the second position652(e.g., logic level 1) having dashed lines inFIG. 6if the electrostatic force and adhesion force642are greater than a spring restoring force644.

FIG. 7illustrates a NEMS device for switching from a second position (e.g., logic level 1) to a first position (e.g., logic level 0). The device700includes a source region710that includes a cantilever712, a drain region720, and a gate region730. The absence of an electrostatic force causes the cantilever712to be restored with a free end of the cantilever moving away from the drain region720if a spring restoring force744is greater than an adhesion force742. The device switches from the second position752(e.g., logic level 1) having dashed lines inFIG. 7to the first position750(e.g., logic level 0) if the spring restoring force744is greater than the adhesion force742.

Typically, NEMS relays are built with a cantilever length of several micrometers down to a few hundreds of nanometers. At the micro scale, the relays can operate close to 1 volt, but at the nano scale the adhesion and restoring forces increase such that the operation voltage is about an order of magnitude higher. Inherent adhesion forces are the primary limitation for low voltage operation of the nano relays at dimension comparable to current MOS transistors.

Embodiments of the present design include at least two long and thin slabs of a magnetic material in the device to partially offset the adhesion forces to have more flexibility on the range of dimensions of the devices and a better tolerance for variations in the gap.

FIG. 8illustrates a NEMS device having nanomagnets for switching from a first position (e.g., logic level 0) to a second position (e.g., logic level 1) in accordance with one embodiment of the present invention. The device800includes a source region810that includes a cantilever812, a drain region820, and a gate region830. The cantilever includes a magnetic material862with dashed lines inFIG. 8while the gate also includes a magnetic material860with dashed lines inFIG. 8. Application of an electrostatic force840causes the cantilever812to bend towards the drain region820with a free end of the cantilever contacting the drain region820if the electrostatic force and adhesion force842are greater than a spring restoring force844and a magnetic force846. The device switches from the first position850(e.g., logic level 0) to the second position852(e.g., logic level 1) having dashed lines inFIG. 8if the electrostatic force and adhesion force842are greater than a spring restoring force844and the magnetic force846.

FIG. 9illustrates a NEMS device having nanomagnets for switching from a second position (e.g., logic level 1) to a first position (e.g., logic level 0) in accordance with one embodiment of the present invention. The device900includes a source region910that includes a cantilever912, a drain region920, and a gate region930. The cantilever includes a magnetic material962with dashed lines inFIG. 9while the gate also includes a magnetic material960with dashed lines inFIG. 9. The absence of an electrostatic force causes the cantilever912to be restored with a free end of the cantilever moving away from the drain region920if a spring restoring force944and a magnetic force946are greater than an adhesion force942. The device switches from the second position952(e.g., logic level 1) having dashed lines inFIG. 9to the first position950(e.g., logic level 0) if the spring restoring force944and the magnetic force are greater than the adhesion force942.

The position, length, thickness, and type of magnetic material can be altered in comparison to the examples ofFIGS. 8 and 9to partially offset the adhesion forces to have more flexibility on the range of dimensions of the devices and a better tolerance for variations in the gap. The nanomagnets can be poled along their long direction with an external magnetic field and afterwards the nanomagnets will remain magnetized in the same direction due to their size and shape. The size ensures that the nanomagnets will be single domain, which is general true regardless of their shape when the nanomagnets are smaller than the typical size of domain walls (e.g., approximately 100 nm). The elongated shape introduces uniaxial shape anisotropy and magnets minimize their energies by aligning their magnetization with the anisotropy easy direction. In fact, since the anisotrophy favor single magnetic domains, elongated nanostructures are single domain up to lengths of approximately 500 nm. This range of lengths of approximately 500 nm or less corresponds with the operational nanorelay lengths of interest. The coercive field of the nanomagnets is large enough to ensure that the nanomagnets do not switch magnetizations when the nanomagnets are in proximity to each other and can be controlled by varying the thickness and hardness of the nanomagnets. It is desirable that the nanomagnets are not closer to each other than about 1 nm since adhesion between metallic surfaces is thirty times or more stronger than van der Waals forces.

FIGS. 10A-10Jillustrate a method with process operations for fabricating a NEMS device with nanomagnets in accordance with one embodiment of the present invention.FIG. 10Aillustrates a process operation with at least one nonmagnetic metal layer1004(e.g., Ta, Ru) being formed (e.g., sputtered) on a silicon substrate1002. The at least one nonmagnetic metal layer can provide a crystallization template (e.g., orientation) for a subsequently grown or sputtered magnetic layer. This nonmagnetic layer can also prevent diffusion from the subsequently grown or sputtered magnetic layer and the silicon substrate.FIG. 10Billustrates a process operation with a ferromagnetic metal layer1006(e.g., Co) being formed (e.g., sputtered) on the at least one nonmagnetic metal layer1004.

FIG. 10Cillustrates a process operation with a dielectric layer1008(e.g., Ta, Ru) being formed (e.g., sputtered) on the ferromagnetic layer1006.FIG. 10Dillustrates a process operation with a dielectric layer1010(e.g., sacrificial oxide) being deposited on the dielectric layer1008.FIG. 10Eillustrates a process operation with a ferromagnetic metal layer1012(e.g., Ta, Ru) being formed (e.g., sputtered) on the dielectric layer1010.

FIG. 10Fillustrates a process operation with a polysilicon layer1014(or semiconductor or metallic layer) being deposited on the ferromagnetic layer1012.FIG. 10Gillustrates process operations with a photoresist layer1016being formed on the polysilicon layer1014, lithography, and then development and removal of the exposed regions of the photoresist.FIG. 10Hillustrates a reactive ion etch (RIE) process operation with regions that are not masked by the photoresist being etched including the polysilicon layer1014and the ferromagnetic metal layer1012.FIG. 10Iillustrates a wet etch process operation with exposed regions of the dielectric layer1010being etched. A cantilever1020is formed based on the RIE and wet etch operations.FIG. 10Jillustrates a process operation with the photoresist being removed to form a NEM device1030that includes nanomagnets1006and1012.

FIG. 11illustrates a block diagram of an electronic system1100, in accordance with an embodiment of the present invention. The electronic system1100can correspond to, for example, a portable system, a computer system, a process control system, or any other system that utilizes a processor and an associated memory. The electronic system1100may include a microprocessor1102(having a processor1104and control unit1106), a memory device1108, and an input/output device1110(it is to be understood that the electronic system1100may have a plurality of processors, control units, memory device units and/or input/output devices in various embodiments). In one embodiment, the electronic system1100has a set of instructions that define operations which are to be performed on data by the processor1104, as well as, other transactions between the processor1104, the memory device1108, and the input/output device910. The control unit1106coordinates the operations of the processor1104, the memory device1108and the input/output device1110by cycling through a set of operations that cause instructions to be retrieved from the memory device1108and executed. The memory device1108can include NEMS devices (e.g., NEMS relays) as described in the present description. In an embodiment, the memory device1108is embedded in the microprocessor102, as depicted inFIG. 11.

FIG. 12illustrates a computing device1200in accordance with one implementation of the invention. The computing device1200houses a board1202. The board1202may include a number of components, including but not limited to a processor1204and at least one communication chip1206. The processor1204is physically and electrically coupled to the board1202. In some implementations the at least one communication chip1206is also physically and electrically coupled to the board1202. In further implementations, the communication chip1206is part of the processor1204.

The processor1204of the computing device1200includes an integrated circuit die1210packaged within the processor1204. In some implementations of the invention, the integrated circuit die of the processor includes one or more devices1212, such as spin transfer torque memory built in accordance with implementations of the invention. The term “processor” may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be stored in registers and/or memory.

The communication chip1206also includes an integrated circuit die1220packaged within the communication chip1206. In accordance with another implementation of the invention, the integrated circuit die of the communication chip includes one or more devices1221, such as NEMS devices built in accordance with implementations of the invention.

In further implementations, another component housed within the computing device1200may contain an integrated circuit die that includes one or more devices, such as NEMS devices built in accordance with implementations of the invention.

Accordingly, one or more embodiments of the present invention relate generally to the NEMS devices having nanomagnets with enhanced operating voltage and improved control of dimensions of a cantilever and a gap between the cantilever and a substrate.

In an embodiment, a nanoelectromechanical (NEMS) device includes a substrate layer, a first magnetic layer disposed above the substrate layer, a first dielectric layer disposed above the first magnetic layer, a second dielectric disposed above the first dielectric layer, and a cantilever disposed above the second dielectric layer. The cantilever bends from a first position to a second position towards the substrate layer when a voltage is applied to the cantilever.

In one embodiment, the cantilever includes a second magnetic layer and a polysilicon layer disposed above the second magnetic layer. The first magnetic layer and the second magnetic layer may include Cobalt (Co).

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to lower an operational voltage of the NEMS device.

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to increase size ranges for a length and a thickness of the cantilever and increase a range of acceptable gaps between the cantilever and the first dielectric layer.

In one embodiment, the cantilever while in the second position contacts the first dielectric layer with the adhesion field applying a force for keeping the cantilever in contact with the first dielectric layer. The cantilever is restored from the second position to the first position having no contact with the first dielectric layer when the voltage is removed from the cantilever.

In one embodiment, the NEMS device further includes a non-magnetic layer disposed above the substrate.

In one embodiment, the nanoelectromechanical (NEMS) device includes a substrate, a source region disposed above or formed in the substrate, a drain region disposed above or formed in the substrate, and a gate region disposed above or formed in the substrate. The gate region includes a first magnetic layer. The source region includes a cantilever having a second magnetic layer with the cantilever bending from a first position to a second position in contact with the drain region when a voltage is applied to the gate region.

In one embodiment, the NEMS device is a relay for switching between the first and second positions.

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to lower an operational voltage of the NEMS device. The first magnetic layer and the second magnetic layer comprise Cobalt (Co).

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to increase size ranges for a length and a thickness of the cantilever and a range of acceptable gaps between the cantilever and the drain region.

In one embodiment, the cantilever includes a free end that contacts the drain region while in the second position with the adhesion field applying a force for keeping the cantilever in contact with the drain region. The cantilever is restored from the second position to the first position having no contact with the drain region when the voltage is removed from the gate region.

In one embodiment, a computing device includes at least one processor for executing instructions of one or more software programs and at least one communication chip communicatively coupled to the at least one processor. The at least one processor or the at least one communication chip further include at least one nanoelectromechanical (NEMS) device that includes

a source region, a drain region, and a gate region having a first magnetic layer. The source region includes a cantilever having a second magnetic layer with the cantilever bending from a first position to a second position in contact with the drain region when a voltage is applied to the gate region.

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to lower an operational voltage of the NEMS device.

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to increase size ranges for a length and a thickness of the cantilever and a range of acceptable gaps between the cantilever and the drain region.

In one embodiment, the cantilever includes a free end that contacts the drain region while in the second position with the adhesion field applying a force for keeping the cantilever in contact with the drain region.

In one embodiment, the cantilever is restored from the second position to the first position having no contact with the drain region when the voltage is removed from the gate region.

In one embodiment, a method for fabricating a nanoelectromechanical (NEMS) device with nanomagnets includes forming at least one nonmagnetic metal layer on a substrate, forming a first ferromagnetic metal layer on the at least one nonmagnetic metal layer, forming a first dielectric layer on the ferromagnetic layer, depositing a second dielectric layer on the first dielectric layer, forming a second ferromagnetic metal layer on the second dielectric layer, depositing a polysilicon layer on the second ferromagnetic layer, and etching regions of the polysilicon layer, the second ferromagnetic layer, and the second dielectric layer that are not masked by the photoresist to form a cantilever that bends from a first position to a second position towards the substrate when a voltage is applied to the cantilever.

In one embodiment, the first and second ferromagnetic layers generate a magnetic field that counteracts an adhesion field to lower an operational voltage of the NEMS device.

In one embodiment, the first and second ferromagnetic layers generate a magnetic field that counteracts an adhesion field to increase size ranges for a length and a thickness of the cantilever and a gap between the cantilever and the first dielectric layer.

In one embodiment, an apparatus includes a means for supporting a first magnetic layer and a dielectric layer. The apparatus also includes a means for switching between a first position and a second position. The means for switching moves from a first position to a second position towards the dielectric layer when a voltage is applied to the means for switching.

In one embodiment, the means for switching comprises a second magnetic layer and a polysilicon layer. The first and second magnetic layers generate a magnetic field that counteracts an adhesion field to lower an operational voltage of the apparatus.

In one embodiment, the first and second magnetic layers generate a magnetic field that counteracts an adhesion field to increase size ranges for a length and a thickness of the means for switching and to increase a range of acceptable gaps between the means for switching and the dielectric layer.