1. A silicon carbide power device equipped with termination structure, comprising:
a silicon carbide substrate including a drift layer which includes a first conductivity and an active zone and a termination zone surrounding the active zone;
a power element structure located in the active zone; and
a termination structure which is located in the termination zone and includes a second conductivity different from the first conductivity, and includes at least one first doped ring abutting and surrounding the power element structure, at least one second doped ring surrounding the first doped ring and at least one ancillary ring which overlaps the first doped ring;
wherein the first doped ring has a first doping concentration smaller than that of the second doped ring and a first doping depth greater than that of the second doped ring, and wherein the ancillary ring has a third doping depth smaller than the first doping depth and a third doping concentration greater than the first doping concentration.
2. The silicon carbide power device of claim 1 further including at least one doped well which is located below the power element structure and includes the second conductivity.
3. The silicon carbide power device of claim 2, wherein the doped well includes a first doped well and a second doped well overlapping the first doped well, the first doped well having a doping depth smaller than that of the second doped well and a doping concentration greater than that of the second doped well.
4. The silicon carbide power device of claim 1, wherein the first doped ring has a doped width smaller than that of the second doped ring.
5. The silicon carbide power device of claim 1, wherein the ancillary ring has a greater third doping width in comparison with the first doped ring.
6. The silicon carbide power device of claim 1, wherein the first doped ring has a first doping width greater than that of the second doped ring.
7. The silicon carbide power device of claim 1, wherein the ancillary ring has a smaller third doping width in comparison with the first doped ring.
8. The silicon carbide power device of claim 1, wherein the ancillary ring has a same third doping width in comparison with the first doped ring.
9. The silicon carbide power device of claim 1, wherein the termination structure includes a plurality of first doped rings spaced from each other at at least one first distance, and a plurality of second doped rings spaced from each other at at least one second distance greater than the first distance.
10. The silicon carbide power device of claim 9, wherein the abutting first doped ring and second doped ring are spaced from each other at a third distance greater than the first distance and smaller than the second distance.
11. The silicon carbide power device of claim 9, wherein the plurality of first doped rings are spaced from each other at a plurality of first distances which gradually increase with increased distances from the power element structure.
12. The silicon carbide power device of claim 9, wherein the plurality of second doped rings are spaced from each other at a plurality of second distances which gradually increase with increased distances from the power element structure.
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 liquid metal droplets comprising the steps of:
a) providing a pool of a molten metal with a free surface,
b) providing a continual flow of an inert gas across the free surface of the pool of molten metal, the continual flow substantially having a gas flow direction at the free surface of the pool,
c) generating ultrasonic acoustic waves with at least one ultrasonic transducer adjacent to the pool of molten metal,
d) focussing the generated ultrasonic acoustic waves to converge near the free surface of the pool of molten metal to emit drops of liquid metal through the continual flow of inert gas using at least one acoustic lens positioned adjacent to the at least one ultrasonic transducer, the emitted drops being emitted in a direction which is substantially transverse to the gas flow direction.
2. The method for forming liquid metal droplets of claim 1 wherein the emitted droplets are emitted in a direction which is substantially orthogonal to the gas flow direction.
3. The method for forming liquid metal droplets of claim 1 further comprising the step of successively depositing the emitted droplets of liquid metal onto a substrate to form a solid structure.
4. The method for forming liquid metal droplets of claim 1 wherein the continual flow of inert gas is at approximately 0.5 msec or less.
5. The method for forming liquid metal droplets of claim 3 wherein the continual flow of inert gas across the free surface also comprises bleeding gas outward from the free surface.
6. The method for forming liquid metal droplets of claim 5 wherein the space between the free surface and the substrate are substantially filled with the inert gas.
7. A method for forming liquid metal droplets comprising the steps of:
a) providing at least two separated pools of liquid metal, each pool having a free surface,
b) providing a single continual flow of inert gas across the free surfaces of the at least two separated pools of liquid metal, the continual flow substantially having a gas flow direction at the free surface of each pool,
c) generating ultrasonic acoustic waves in at least one pool with at least one ultrasonic transducer associated with the at least one pool,
d) focussing the generated ultrasonic waves to converge near the free surface of the at least one pool to emit drops of liquid metal through the continual flow of inert gas using at least one acoustic lens positioned adjacent to the at least one ultrasonic transducer, the emitted drops being emitted in a direction which is substantially transverse to the gas flow direction.
8. The method for forming liquid metal droplets of claim 7 wherein the emitted liquid metal droplets are emitted in a direction which is substantially orthogonal to the gas flow direction.
9. The method for forming liquid metal droplets of claim 7 further comprising the step of successively depositing the emitted droplets of liquid metal onto a substrate to form a solid structure.
10. The method for forming liquid metal droplets of claim 7 wherein the continual flow of inert gas is at approximately 0.5 msec or less.
11. The method for forming liquid metal droplets of claim 9 wherein the continual flow of inert gas across the free surface also comprises bleeding gas outward from the free surface.
12. The method of forming liquid metal droplets of claim 11 wherein the space between the free surface and the substrate are substantially filled with the inert gas.
13. A device emitting liquid metal droplets on demand from a free surface of a liquid pool comprising:
a) a solid substrate having first and second surfaces, and having an acoustic focussing element on the first surface,
b) acoustic wave generating means intimately coupled to the second surface of said solid substrate for generating RF acoustic waves such that the acoustic focussing element causes an acoustic beam to be focussed to converge near the free surface of the liquid pool, for forming droplets of the liquid,
c) a top liquid control plate, having first and second surfaces, with the first surface in intimate contact with the liquid pool, said top fluid control plate have at least one opening therethrough, the opening being aligned with said acoustic wave generating means and the acoustic focussing element such that the acoustic beam focussed near the free surface of the pool will be focussed at least partly within the opening, the opening being large enough to permit droplets formed by the focussing of the acoustic beam at the free surface of the liquid to pass therethrough,
d) a top gas containment plate have first and second surfaces to at least partially contain an inert gas between the first surface of the top gas containment plate and the second surface of the top fluid control plate, said top gas containment plate having at least one opening therethrough, the opening in the top gas containment plate being aligned with the opening in the top fluid control plate such that any liquid drops passing through the opening in the top fluid control plate may also pass through the top gas containment plate.