1. A semiconductor device comprising:
a first silicon germanium layer formed on a single crystalline silicon substrate, the first silicon germanium layer having a concentration gradient of germanium;
a second silicon germanium layer formed on the first silicon germanium layer, the second silicon germanium layer having a concentration of germanium in a range of about 1 percent by weight to about 15 percent by weight based on the total weight of the second silicon germanium layer;
a strained silicon layer formed on the second silicon germanium layer;
an isolation layer formed at a first portion of the strained silicon layer to define an isolation region;
a gate structure formed on the isolation region of the strained silicon layer; and
sourcedrain regions formed at second portions of the strained silicon layer adjacent to the gate structure.
2. The semiconductor device of claim 1, wherein a germanium concentration in the first silicon germanium layer gradually increases from a lower portion of the first silicon germanium layer to an upper portion of the first silicon germanium layer.
3. The semiconductor device of claim 2, wherein the germanium concentration at a top portion of the first silicon germanium layer is substantially the same as that in the second silicon germanium layer.
4. The semiconductor device of claim 1,. wherein the strained silicon layer has a thickness of about 1,000 \u212b to about 5,000 \u212b.
5. The semiconductor device of claim 1, wherein the sourcedrain regions have junction depths substantially smaller than a thickness of the strained silicon layer.
6. The semiconductor device of claim 1, wherein the isolation layer has a thickness less than about 90% of a thickness of the strained silicon layer.
7. A method of manufacturing a semiconductor device comprising steps of:
forming a first silicon germanium layer on a single crystalline silicon substrate, wherein the first silicon germanium layer has a concentration gradient of germanium;
forming a second silicon germanium layer on the first silicon germanium layer, wherein the second silicon germanium layer has a concentration of germanium in a range of about 1 percent by weight to about 15 percent by weight based on the total weight of the second silicon germanium layer;
forming a strained silicon layer on the second silicon germanium layer;
forming an isolation layer at a first portion of the strained silicon layer to define an isolation region;
forming a gate structure on the isolation region of the strained silicon layer; and
forming sourcedrain regions at second portions of the strained silicon layer adjacent to the gate structure.
8. The method of claim 7, wherein the first silicon germanium layer is formed by an epitaxial growth process to provide a concentration gradient of germanium that gradually increases from a lower portion of the first silicon germanium layer to an upper portion of the first silicon germanium layer.
9. The method of claim 7, wherein the concentration of germanium in a top portion of the first silicon germanium layer is substantially the same as that in the second silicon germanium layer.
10. The method of claim 7, wherein the sourcedrain regions are formed by an ion implantation process to have junction depths substantially smaller than a thickness of the strained silicon layer.
11. The method of claim 7, wherein the strained silicon layer is formed to a thickness of about 1,000 \u212b to about 5,000 \u212b.
12. The method of claim 7, wherein the steps of forming the isolation layer further comprises steps of:
forming a buffer oxide layer pattern and a hard mask pattern on the strained silicon layer;
forming a trench at an upper portion of the strained silicon layer by partially etching the strained silicon layer using the hard mask pattern as an etching mask; and
forming the isolation layer to fill up the trench.
13. The method of claim 12, further comprising a step of cleaning the strained silicon layer using a cleaning solution after the isolation layer has been formed.
14. The method of claim 12, wherein the isolation layer is formed to have a thickness less than about 90% of a thickness of the strained silicon layer.
15. A transistor comprising:
a first silicon germanium layer formed on a single crystalline silicon substrate, the first silicon germanium layer having a concentration gradient of germanium that ranges from substantially zero at an interface between the first silicon germanium layer and the silicon substrate up to a germanium concentration that is substantially identical to that in a second silicon germanium layer at an interface between the first and the second silicon germanium layers;
a second silicon germanium layer formed on the first silicon germanium layer, the second silicon germanium layer having a concentration of germanium in a range of about 1 percent by weight to about 15 percent by weight based on the total weight of the second silicon germanium layer;
a strained silicon layer formed on the second silicon germanium layer;
an isolation layer formed at a first portion of the strained silicon layer to define an isolation region;
a gate structure formed on the isolation region of the strained silicon layer; and
sourcedrain regions formed at second portions of the strained silicon layer adjacent to the gate structure.
16. The transistor of claim 15, wherein the strained silicon layer has a thickness of about 1,000\u212b to about 5,000 \u212b.
17. The transistor of claim 15, wherein the sourcedrain regions have junction depths substantially smaller than a thickness of the strained silicon layer.
18. The transistor of claim 15, wherein the isolation layer has a thickness less than about 90% of a thickness of the strained silicon layer.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. A motor defining an axial direction, the motor comprising:
a plurality of core pairs, each of the core pairs consisting of an inner core and an outer core, arranged next to each other along the axial direction such that the inner cores are in contact with each other;
a coil wound around each of the core pairs; and
a case formed from a magnetic material that covers the coils wherein the case is welded to at least the inner cores to form two independent magnetic circuits formed by the inner cores, the case and the outer cores.
2. A motor according to claim 1, wherein the case is welded to the outer cores.
3. A motor according to claim 1, wherein each of the inner cores and each of the outer cores has teeth-like poles;
the teeth-like poles on the inner cores and the teeth-like poles on the outer cores are alternately disposed to face a rotor magnet of a rotor that is disposed inside the plurality of core pairs; and
the case is commonly affixed to outer circumference sections of the inner cores and outer cores that form the plurality of core pairs.
4. A motor according to claim 3, wherein the case is formed from a curled thin plate.
5. A motor according to claim 4, further comprising connection terminals to supply current to the coils connected to the inner cores and the outer cores, wherein the case has an arc-shape to leave an opening for the connection terminals.
6. A motor according to claim 5, wherein the arc-shaped case has end sections, and the case and the inner cores are welded at welding spots at the end sections of the arc-shaped case and at a midpoint in the circumferential direction between the end sections of the arc-shaped case.