1. A microelectromechanical (MEM) device, comprising:
a substrate having a surface;
a structure coupled to, and movably suspended above, the substrate surface;
a first stop element coupled to the structure and movable therewith; and
a protective cap coupled to the substrate and including a second stop element, the second stop element spaced apart from the first stop element,
whereby the first and second stop elements together limit movement of the structure in at least three orthogonal axes.
2. The MEM device of claim 1, wherein:
the first stop structure defines a travel stop that includes at least an inner peripheral surface that defines a cavity; and
the second stop structure defines a protective cap stop section, the protective cap stop section disposed at least partially within the travel stop cavity and spaced apart from the travel stop inner peripheral surface,
3. The MEM device of claim 2, wherein the protective cap stop section is spaced:
a first predetermined distance from the travel stop inner peripheral surface along a first of the three orthogonal axes;
a second predetermined distance from the travel stop inner peripheral surface along a second of the three orthogonal axes; and
a third predetermined distance from the travel stop inner peripheral surface along a third of the three orthogonal axes.
4. The MEM device of claim 3, wherein at least the first and second predetermined distances are substantially equivalent.
5. The MEM device of claim 3, wherein the first, second, and third predetermined distances are substantially equivalent.
6. The MEM device of claim 1, wherein:
the MEM device is an accelerometer; and
the structure is a seismic mass.
7. The MEM device of claim 1, wherein:
the structure includes an outer surface; and
the first stop element is formed on the structure outer surface.
8. The MEM device of claim 1, wherein the first stop element is integrally formed as part of the structure.
9. The MEM device of claim 2, wherein the protective cap stop section is spaced a predetermined distance from the travel stop inner peripheral surface.
10. The MEM device of claim 9, wherein the predetermined distance is defined by a thickness of a layer of sacrificial material removed from between the travel stop and the protective cap stop section.
11. The MEM device of claim 1, further comprising:
a layer of an electrical isolation material disposed between the protective cap and the substrate.
12. A method of forming a microelectromechanical (MEM) device on a substrate including a handle layer, an active layer, and a sacrificial layer disposed at least partially therebetween, the method comprising the steps of:
forming at least a structure in the active layer;
removing at least a portion of the sacrificial layer to thereby release the structure from the substrate;
forming a first stop element on the structure; and
forming a protective cap over at least a portion of the travel stop, the protective cap including a second stop element spaced apart from the first stop element.
13. The method of claim 12, wherein:
the first stop element defines a travel stop that includes at least an inner peripheral surface that defines a cavity; and
the second stop element defines stop section disposed at least partially within the travel stop cavity.
14. The method of claim 12, further comprising:
forming a plurality of etch openings in the active layer to thereby form the structure therein;
forming a layer of sacrificial material into the etch openings and over a portion of the structure outer surface; and
following formation of the first stop element, exposing the formed layer of sacrificial material and the sacrificial layer to an etchant, whereby the first layer of sacrificial material and the sacrificial layer are removed.
14. The method of claim 12, further comprising:
forming a layer of sacrificial material over at least a portion of the first stop element, the layer of sacrificial material having a predetermined thickness that, upon removal thereof, defines a predetermined distance between the first and second stop elements.
15. The method of claim 11, further comprising:
forming a layer of electrical isolation material on at least a portion of the active layer;
forming the protective cap on the layer of electrical isolation material.
16. The method of claim 12, further comprising:
forming a plurality of etch openings in the active layer to thereby form the structure therein;
forming a first layer of sacrificial material in the etch openings and over a portion of the structure outer surface;
following formation of the first stop element, forming a second layer of sacrificial material over the first layer of sacrificial material and over a portion of the first stop element;
forming a third layer of sacrificial material over the second layer of sacrificial material, the third layer of sacrificial material having a predetermined thickness that, upon removal thereof, defines a predetermined distance between the first and second stop elements; and
following formation of the first stop element, exposing the first, second, and third layers of sacrificial material and the sacrificial layer to an etchant, whereby the first, second, and third layers of sacrificial material and the sacrificial layer are removed.
17. The method of claim 13, wherein the protective cap stop section is spaced:
a first predetermined distance from the travel stop inner peripheral surface along a first of the three orthogonal axes;
a second predetermined distance from the travel stop inner peripheral surface along a second of the three orthogonal axes; and
a third predetermined distance from the travel stop inner peripheral surface along a third of the three orthogonal axes.
18. The method of claim 17, wherein at least the first and second predetermined distances are substantially equivalent.
19. The method of claim 17, wherein the first, second, and third predetermined distances are substantially equivalent.
20. The method of claim 12, wherein:
the MEM device is an accelerometer; and
the structure is a seismic mass.
21. The method of claim 12, wherein:
the formed structure includes an outer surface; and
the first stop element is formed on the structure outer surface.
22. A microelectromechanical (MEM) device, comprising:
a substrate having a surface;
a structure coupled to, and movably suspended above, the substrate surface;
a travel stop coupled to the structure and movable therewith, the travel stop including at least an inner peripheral surface that defines a cavity; and
a protective cap coupled to the substrate and including a stop section, the protective cap stop section disposed at least partially within the travel stop cavity and spaced apart from the travel stop inner peripheral surface,
whereby the travel stop and the protective cap stop section together limit movement of the structure in at least three orthogonal axes.
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 continuous process for the selective preparation of acetic acid from a gaseous feed of ethane, ethylene or mixtures thereof and oxygen at elevated temperature, in which the gaseous feed is brought together with a catalyst comprising the elements Mo, Pd, X and Y in gram-atom ratios a:b:c:d in combination with oxygen
MoaPdbXcYd\u2003\u2003I
where the symbols X and Y are as defined below:
X is one or more elements selected from the group consisting of Cr, Mn, Ta, Ti, V, Te and W,
Y is one or more elements selected from the group consisting of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Ti and U but shall be at least Nb;
the indices a, b, c and d are the gram-atom ratios of the corresponding elements, where
a=1;
b=from 0.0001 to 0.01;
c=from 0.04 to 1; and
d=from 0.005 to 1,
and in which the residence times and the composition of the gaseous feed are selected in such a way that the space-time yield in the oxidation to acetic acid is >470 kg(hm3), with the proviso that the catalyst is obtained by the use of a niobium ammonium carboxylate as niobium source.
2. The process of claim 1, wherein niobium ammonium oxalate is used as niobium source.
3. The process of claim 1, wherein the temperature is in the range from 200 to 500\xb0 C.
4. The process of claim 1, wherein the pressure in the reactor is in the range from 1 to 50 bar.
5. The process of claim 1, wherein b is in the range from 0.0001 to 0.001.
6. The process of claim 1, wherein ethane mixed with at least one further gas is fed to the reactor.
7. The process as claimed in claim 6, wherein the further gas fed in is nitrogen, oxygen, methane, carbon monoxide, carbon dioxide, ethylene andor steam.
8. The process of claim 1, wherein the catalyst is mixed with a support material or immobilized on a support material.
9. The process of claim 1, wherein the selectivity of the oxidation reaction of ethane andor ethylene to acetic acid is >70 mol %.
10. The process of claim 1, wherein the catalyst comprises Pd introduced in the form of an alcoholic solution of palladium acetate.
11. A catalyst for the selective oxidation of ethane, ethylene or mixtures thereof and oxygen, comprising the elements Mo, Pd, X and Y in gram-atom ratios a:b:c:d in combination with oxygen
MoaPdbXcYd\u2003\u2003I
where the symbols X and Y are as defined below:
X is one or more elements selected from the group consisting of Cr, Mn, Ta, Ti, V, Te and W,
Y is one or more elements selected from the group consisting of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Ti and U but shall be at least Nb;
the indices a, b, c and d are the gram-atom ratios of the corresponding elements, where
a=1;
b=from 0.0001 to 0.01;
c=from 0.04 to 1; and
d=from 0.005 to 1,
the space-time yield in the oxidation reaction is >470 kg(hm3), with the proviso that the catalyst is obtainable by the use of a niobium ammonium carboxylate as niobium source.
12. A catalyst as claimed in claim 11, where niobium oxalate is used as niobium source.
13. The catalyst as claimed in claim 11, where the Pd has been introduced in the form of an alcoholic solution of palladium acetate.
14. A continuous process for the selective preparation of acetic acid from a gaseous feed of ethane, ethylene or mixtures thereof and oxygen at elevated temperature, in which the gaseous feed is brought together with a catalyst comprising the elements Mo, Pd, X and Y in gram-atom ratios a:b:c:d in combination with oxygen
MoaPdbXcYd\u2003\u2003I
where the symbols X and Y are as defined below:
X is one or more elements selected from the group consisting of Cr, Mn, Ta, Ti, V, Te and W,
Y is one or more elements selected from the group consisting of B, Al, Ga, In, Pt, Zn, Cd, Bi, Ce, Co, Rh, Ir, Cu, Ag, Au, Fe, Ru, Os, K, Rb, Cs, Mg, Ca, Sr, Ba, Nb, Zr, Hf, Ni, P, Pb, Sb, Si, Sn, Ti and U but shall be at least Nb;
the indices a, b, c and d are the gram-atom ratios of the corresponding elements, where
a=1;
b=from 0.0001 to 0.01;
c=from 0.04 to 1; and
d=from 0.005 to 1,
and in which the residence times and the composition of the gaseous feed are selected in such a way that the space-time yield in the oxidation to acetic acid is >470 kg(hm3), with the proviso that the catalyst is obtainable by the use of a niobium ammonium oxalate as niobium source and that Pd is introduced in the form of an alcoholic solution of palladium acetate.