1. A seal assembly for a rotary machine, the seal assembly comprising: a plurality of sealing device segments disposed circumferentially intermediate to a stationary housing and a rotor, wherein each of the plurality of sealing device segments comprises: a stator interface element; a shoe plate comprising one or more labyrinth teeth facing the rotor and a load bearing surface region, wherein the shoe plate is configured to allow a high pressure fluid to an upstream portion of forwardmost labyrinth tooth and a low pressure fluid to a downstream portion of the aftmost labyrinth tooth and further configured to generate an aerodynamic force between the shoe plate and the rotor, a secondary seal configured to be in contact with the stator interface element at a radially outer end and configured to be in contact with an elevated nose of the shoe plate on a radially inner end, wherein the secondary seal comprises an outer layer section and an inner layer section such that each of the outer layer section of the secondary seal having an circumferentially overhanging portion overlaps a sealing device segment gap formed between inner layer section of adjacent secondary seal segments; and a plurality of bellow springs or flexures attached to the shoe plate and to the stator interface element, wherein the shoe plate comprises the one or more labyrinth teeth located towards a front end of the shoe plate for separating a high pressure side from a low pressure side in the rotary machine and one or more ports for allowing flow of low pressure fluid from the downstream portion of aftmost labyrinth tooth to a rear cavity formed by the plurality of bellow springs or flexures, the stator interface element and the shoe plate.
2. The seal assembly of claim 1, wherein the load bearing surface region of the shoe plate comprises one or more grooves or pockets on a side facing the rotor for generating an aerodynamic force.
3. The seal assembly of claim 1, wherein the load bearing surface region of the shoe plate has a radius larger than the rotor radius resulting in a formation of convergent or convergent-divergent fluid film in a tangential direction for generation of an aerodynamic force.
4. The seal assembly of claim 1, wherein the load bearing surface region and the rotor comprises a wear-resistant coating or a layer of lubricating coating on surfaces facing each other.
5. The seal assembly of claim 1, wherein the one or more ports are angled for allowing flow of the low pressure fluid in a radial direction from behind the aftmost labyrinth tooth into the rear cavity formed by the plurality of bellow springs or flexures, the stator interface element and the shoe plate.
6. The seal assembly of claim 1, wherein, the one or more ports are angled for allowing flow of the low pressure fluid in a circumferential direction causing the fluid to swirl as the fluid transfers from behind the aftmost labyrinth tooth to radially above the shoe plate.
7. The seal assembly of claim 1, wherein the shoe plate comprises a L-shaped structure with an elevated nose section for contact with the secondary seal segment.
8. The seal assembly of claim 7, wherein the L-shaped structure comprises one or more labyrinth teeth located towards a front end of the shoe plate for separating a high pressure side from a low pressure side and one or more ports for allowing flow of low pressure fluid from the downstream portion of aftmost labyrinth tooth to a rear cavity formed by the plurality of bellow springs or flexures, the stator interface element and the shoe plate.
9. The seal assembly of claim 7, wherein the L-shaped structure comprises one or more labyrinth teeth located towards a backward end of the shoe plate for separating a high pressure side from a low pressure side and one or more ports for allowing flow of high pressure fluid from a front cavity formed by the plurality of bellow springs or flexures, the stator interface element and the shoe plate to an upstream portion of frontmost labyrinth tooth.
10. The seal assembly of claim 1, wherein the shoe plate comprises one or more axial ribs.
11. The seal assembly of claim 1, wherein each of the sealing device segments comprises feeding grooves oriented axially on both sides of the load-bearing surface region of the shoe plate.
12. The seal assembly of claim 1, where the rotor comprises grooves or slots or pockets rotor angled in axial direction or combined axial and tangential direction or in a herringbone pattern, for generating an aerodynamic force.
13. The seal assembly of claim 12, wherein the grooves or slots or pockets or the herringbone pattern on the rotor are aligned in the direction of rotation or opposite to the direction of rotation.
14. The seal assembly of claim 1, further comprising a labyrinth teeth clearance more than a load bearing surface region clearance.
15. The seal assembly of claim 1, wherein the stator interface element comprises one or more grooves or slots for allowing disposal of one or more spline seal shims for reducing segment-gap leakage between stator interface elements of neighboring sealing device segments.
16. The seal assembly of claim 1, wherein the shoe plate comprises one or more pressurization ports located axially for allowing flow of the high pressure fluid to a rotor-shoe gap.
17. The seal assembly of claim 1, wherein the shoe plate comprises grooves or slots for allowing disposal of spline seal shims for reducing segment-gap leakages between shoe plates of neighboring sealing device segments.
18. The seal assembly of claim 1, wherein a location of the contact between the secondary seal and the stator interface element at the radially outer end, a location of the contact between the secondary seal with the shoe plate at the radially inner end; and an attachment location of the plurality of bellow springs or flexures to the shoe plate and to the stator interface element are at predetermined positions based on ensuring that a line of action of an effective axial force passes through the plurality of bellow springs or flexures at about the radial midspan of the bellow springs or flexures in order to attain a zero or small front-aft tilt of the shoe plate.
19. The seal assembly of claim 1, wherein the secondary seal is tilted with respect to a direction perpendicular to an axial direction of the rotary machine to include an optimum angle for attaining an almost constant magnitude of contact force for compensating the reduced contact force caused by reduction in effective length of the secondary seal.
20. The seal assembly of claim 1, wherein the secondary seal comprises an inner layer section with a slanted profile for maintaining a constant force between the secondary seal segment and the shoe plate at the line contact during radial motion of the shoe plate.
21. A rotary machine, comprising:
a rotor;
a stationary housing; and
a seal assembly according to claim 1.
22. The rotary machine of claim 21, wherein the contact between the secondary seal and the stator interface element at the radially outer end, the contact between the secondary seal with the shoe plate and the radially inner end; and the attachment of the plurality of bellow springs or flexures to the shoe plate and to the stator interface element are at predetermined positions based on ensuring thata line of action of an effective axial force passes through the plurality of bellow springs or flexures at about the radial midspan of the plurality of bellow springs or flexures in order to attain a zero or small front-aft tilt of the shoe plate.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A method for forming an asymmetric memory cell, the method comprising:
forming a bottom electrode having a first area;
forming an electrical pulse various resistance (EPVR) material overlying the bottom electrode;
forming a top electrode overlying the EPVR layer having a second area, less than the first area.
2. The method of claim 1 further comprising:
inducing an electric field between the top electrode and the bottom electrode; and,
in response to the electric field, inducing current flow through the EPVR adjacent the top electrode.
3. The method of claim 2 further comprising:
in response to inducing current flow through the EPVR adjacent the top electrode, modifying the resistance of the EPVR between the top and bottom electrodes.
4. The method of claim 3 wherein inducing an electric field between the top electrode and the bottom electrode includes applying a negative voltage pulse between the top and bottom electrodes having an amplitude in the range of 2 to 5 volts and a time duration in the range of 1 nanosecond (ns) to 10 microseconds (s); and,
wherein modifying the resistance of the EPVR between the top and bottom electrodes includes creating a first, high resistance between the electrodes.
5. The method of claim 4 wherein inducing an electric field between the top electrode and the bottom electrode includes applying a positive pulse between the top and bottom electrodes having an amplitude in the range of 2 to 5 volts and a time duration in the range of 1 ns to 10 s; and,
wherein modifying the resistance of the EPVR between the top and bottom electrodes includes creating a second resistance between the electrodes, lower than the first resistance.
6. The method of claim 1 wherein forming a top electrode overlying the CMR layer having a second area, less than the first area, includes the second area being at least 20% smaller than the first area.
7. The method of claim 1 wherein forming a bottom electrode includes forming the bottom electrode from a material selected from the group including Pt, TiN, TaN, TiAlN, TaAlN, Ag, Au, and Ir; and,
wherein forming a top electrode includes forming the top electrode from a material selected from the group including Pt, TiN, TaN, TiAlN, TaAlN, Ag, Au, and Ir.
8. The method of claim 1 wherein forming an EPVR layer includes forming an EPVR layer from a material selected from the group including colossal magnetoresistance (CMR), high temperature super conducting (HTSC), and perovskite metal oxide materials.
9. The method of claim 3 wherein modifying the resistance of the EPVR between the top and bottom electrodes in response to inducing current flow through the EPVR adjacent the top electrode includes modifying the resistance within the range of 100 ohms to 10 mega-ohms.
10. A method for forming an asymmetric memory cell, the method comprising:
forming a bottom electrode having a first area;
forming an electrical pulse various resistance (EPVR) material overlying the bottom electrode;
forming a top electrode overlying the EPVR layer having a second area, greater than the first area.
11. The method of claim 10 wherein forming a top electrode overlying the CMR layer having a second area, greater than the first area, includes the first area being at least 20% smaller than the second area.
12. An asymmetric memory cell comprising:
a bottom electrode having a first area;
an electrical pulse various resistance (EPVR) material layer overlying the bottom electrode; and,
a top electrode overlying the EPVR layer having a second area less than the first area.
13. The memory cell of claim 12 wherein the top electrode second area is at least 20% less than the bottom electrode first area.
14. The memory cell of claim 13 wherein the bottom electrode is a material selected from the group including Pt, TiN, TaN, TiAlN, TaAlN, Ag, Au, and Ir; and,
wherein the top electrode is a material selected from the group including Pt, TiN, TaN, TiAlN, TaAlN, Ag, Au, and Ir.
15. The memory cell of claim 13 wherein the EPVR layer has a first overall resistance, as measured between the top and bottom electrodes, responsive to a first voltage pulse, applied between the top and bottom electrodes; and,
wherein the EPVR layer has a second overall resistance, less than the first resistance, responsive to a second voltage pulse.
16. The memory cell of claim 15 wherein the EPVR layer first resistance is in the range of 100 ohms to 10 mega-ohms, responsive to the first voltage pulse having an negative amplitude in the range of 2 to 5 volts and a time duration in the range of 1 nanosecond (ns) and 10 microseconds (s).
17. The memory cell of claim 16 wherein the EPVR layer second resistance is in the range of 100 ohms to 1 kohm, responsive to the second voltage pulse having an positive amplitude in the range of 2 to 5 volts and a time duration in the range of 1 ns to 10 s.
18. The memory cell of claim 12 wherein the EPVR layer is a material selected from the group including colossal magnetoresistance (CMR), high temperature super conducting (HTSC), and perovskite metal oxide materials.
19. An asymmetric memory cell comprising:
a bottom electrode having a first area;
an electrical pulse various resistance (EPVR) material layer overlying the bottom electrode; and,
a top electrode overlying the EPVR layer having a second area greater than the first area.
20. The memory cell of claim 19 wherein the bottom electrode first area is at least 20% less than the top electrode second area.