Pixel of micro display having vertically stacked sub-pixels and common electrode
View Patent ↗Disclosed is a unit pixel of a microdisplay. In the unit pixel, sub-pixels which respectively form blue, green, and red light are vertically stacked on a growth substrate. Accordingly, the overall area of the unit pixel is reduced, and a transfer process is easily performed.
1. A unit pixel of a microdisplay, the unit pixel comprising:
a first sub-pixel formed on a growth substrate and configured to form light having a first wavelength according to a first current;
a first current blocking layer formed on the first sub-pixel and configured to block a leakage current directed toward the first sub-pixel or introduced from the first sub-pixel;
a second sub-pixel formed on the first current blocking layer and configured to form light having a second wavelength longer than the first wavelength according to a second current;
a second current blocking layer formed on the second sub-pixel and configured to block a leakage current directed toward the second sub-pixel or introduced from the second sub-pixel; and
a third sub-pixel formed on the second current blocking layer and configured to form light having a third wavelength longer than the second wavelength according to a third current,
wherein a common anode is commonly connected to the first sub-pixel, the second sub-pixel, and the third sub-pixel, a first cathode is connected to the first sub-pixel, a second cathode is connected to the second sub-pixel, and a third cathode is connected to the third sub-pixel.
2. The unit pixel of claim 1 , wherein the first current blocking layer is made of a p-type semiconductor or an insulating material.
3. The unit pixel of claim 2 , wherein the first current blocking layer includes p-type GaN, p-type AlGaN, Mg-doped GaN, or SiO 2 .
4. The unit pixel of claim 1 , wherein the second current blocking layer is made of a p-type semiconductor or an insulating material.
5. The unit pixel of claim 4 , wherein the second current blocking layer includes p-type GaN, p-type AlGaN, Mg-doped GaN, or SiO 2 .
6. The unit pixel of claim 1 , wherein the first sub-pixel includes:
a first contact n-type semiconductor layer formed on the growth substrate;
a first tunnel junction layer formed on the first contact n-type semiconductor layer;
a first p-type semiconductor layer formed on the first tunnel junction layer;
a first active layer formed on the first p-type semiconductor layer and configured to form the light having the first wavelength; and
a first n-type semiconductor layer formed on the first active layer,
wherein the common anode is formed on the first contact n-type semiconductor layer and the first cathode is formed on the first n-type semiconductor layer.
7. The unit pixel of claim 6 , wherein the first tunnel junction layer includes:
a first high-concentration n-type semiconductor layer formed on the first contact n-type semiconductor layer; and
a first high-concentration p-type semiconductor layer formed on the first high-concentration n-type semiconductor layer,
wherein, in the direction of the first current flowing during a light emission operation of the first sub-pixel, the first tunnel junction layer is in a reverse-biased state.
8. The unit pixel of claim 6 , wherein the first n-type semiconductor layer forms a p-n junction with the first current blocking layer, wherein the first n-type semiconductor layer and the first current blocking layer forms a reverse-biased junction in the direction of the first current.
9. The unit pixel of claim 1 , wherein the second sub-pixel includes:
a second contact n-type semiconductor layer formed on the first current blocking layer;
a second tunnel junction layer formed on the second contact n-type semiconductor layer;
a second p-type semiconductor layer formed on the second tunnel junction layer;
a second active layer formed on the second p-type semiconductor layer and configured to form the light having the second wavelength; and
a second n-type semiconductor layer formed on the second active layer,
wherein the common anode is formed on the second contact n-type semiconductor layer and the second cathode is formed on the second n-type semiconductor layer.
10. The unit pixel of claim 9 , wherein the second tunnel junction layer includes:
a second high-concentration n-type semiconductor layer formed on the second contact n-type semiconductor layer; and
a second high-concentration p-type semiconductor layer formed on the second high-concentration n-type semiconductor layer,
wherein, in the direction of the second current flowing during a light emission operation of the second sub-pixel, the second tunnel junction layer is in a reverse-biased state.
11. The unit pixel of claim 9 , wherein:
the second n-type semiconductor layer forms a p-n junction with the second current blocking layer, wherein the second n-type semiconductor layer and the second current blocking layer forms a reverse-biased junction in the direction of the second current; and
the second contact n-type semiconductor layer and the first current blocking layer forms a reverse-biased junction in the direction of the second current.
12. The unit pixel of claim 1 , wherein the third sub-pixel includes:
a third n-type semiconductor layer formed on the second current blocking layer;
a third active layer formed on the third n-type semiconductor layer; and
a third p-type semiconductor layer formed on the third active layer,
wherein the common anode covers the third p-type semiconductor layer and the third cathode is formed on the third n-type semiconductor layer.
13. The unit pixel of claim 12 , wherein the third n-type semiconductor layer forms a p-n junction with the second current blocking layer, wherein the third n-type semiconductor layer and the second current blocking layer forms a reverse-biased junction in the direction of the third current.
14. The unit pixel of claim 1 , wherein the second sub-pixel includes:
a first n-type semiconductor layer formed on the first current blocking layer;
a second active layer formed on the first n-type semiconductor layer;
a second p-type semiconductor layer formed on the second active layer;
a second tunnel junction layer formed on the second p-type semiconductor layer; and
a second contact n-type semiconductor layer formed on the second tunnel junction layer,
wherein the common anode is formed on the second contact n-type semiconductor layer and the second cathode is formed on the second n-type semiconductor layer.
15. The unit pixel of claim 14 , wherein:
the second n-type semiconductor layer forms a p-n junction with the first current blocking layer, wherein the second n-type semiconductor layer and the first current blocking layer forms a reverse-biased junction in a direction of the second current; and
the second contact n-type semiconductor layer and the second current blocking layer forms a reverse-biased junction in the direction of the second current.
16. A unit pixel of a microdisplay, the unit pixel comprising:
a first sub-pixel formed on a growth substrate and configured to form light having a first wavelength according to a first current;
a first current blocking layer formed on the first sub-pixel and configured to block a leakage current directed toward the first sub-pixel or introduced from the first sub-pixel;
a second sub-pixel formed on the first current blocking layer and configured to form light having a second wavelength longer than the first wavelength according to a second current; and
a third sub-pixel formed on the second sub-pixel and configured to form light having a third wavelength longer than the second wavelength according to a third current,
wherein a common cathode is commonly connected to the first sub-pixel, the second sub-pixel, and the third sub-pixel, a first anode is connected to the first sub-pixel, a second anode is connected to the second sub-pixel, and a third anode is connected to the third sub-pixel.
17. The unit pixel of claim 16 , wherein the first sub-pixel includes:
a first n-type semiconductor layer formed on the growth substrate;
a first active layer formed on the first n-type semiconductor layer;
a first p-type semiconductor layer formed on the first active layer;
a first tunnel junction layer formed on the first p-type semiconductor layer; and
a first contact n-type semiconductor layer formed on the first tunnel junction layer,
wherein the common cathode is formed on the first n-type semiconductor layer and the first anode is formed on the first contact n-type semiconductor layer.
18. The unit pixel of claim 16 , wherein, in order to block a leakage current between the second current and the third current, a second current blocking layer made of p-type GaN, P-type AlGaN, Mg-doped GaN, or SiO 2 is further included between the second sub-pixel and the third sub-pixel.
19. The unit pixel of claim 18 , wherein the second sub-pixel includes:
a second n-type semiconductor layer formed on the first current blocking layer;
a second active layer formed on the second n-type semiconductor layer;
a second P-type semiconductor layer formed on the second active layer;
a second tunnel junction layer formed on the second p-type semiconductor layer; and
a second contact n-type semiconductor layer formed on the second tunnel junction layer,
wherein the common cathode is formed on the second n-type semiconductor layer and the second anode is formed on the second contact n-type semiconductor layer.
20. The unit pixel of claim 18 , wherein the third sub-pixel includes:
a third n-type semiconductor layer formed on the second current blocking layer;
a third active layer formed on the third n-type semiconductor layer; and
a third P-type semiconductor layer formed on the third active layer,
wherein the common cathode is formed on the third n-type semiconductor layer and the third anode covers the third p-type semiconductor layer.
21. The unit pixel of claim 16 , wherein the second sub-pixel and the third sub-pixel share a common n-type semiconductor layer,
the second sub-pixel includes:
a second contact n-type semiconductor layer formed on the first current blocking layer;
a second tunnel junction layer formed on the second contact n-type semiconductor layer;
a second p-type semiconductor layer formed on the second tunnel junction layer;
a second active layer formed on the second p-type semiconductor layer; and
the common n-type semiconductor layer formed on the second active layer, and
the third sub-pixel includes:
the common n-type semiconductor layer formed on the second active layer;
a third active layer formed on the common n-type semiconductor layer; and
a third p-type semiconductor layer formed on the third active layer,
wherein the common cathode is formed on the common n-type semiconductor layer, the second anode is formed on the second contact n-type semiconductor layer, and the third anode is formed while covering the third p-type semiconductor layer.
22. The unit pixel of claim 16 , wherein a bonding layer is further included between the second sub-pixel and the third sub-pixel.
23. The unit pixel of claim 22 , wherein the third sub-pixel includes:
a third p-type semiconductor layer formed on the bonding layer;
a third active layer formed on the third p-type semiconductor layer; and
a third n-type semiconductor layer formed on the third active layer,
wherein the common cathode covers the third n-type semiconductor layer and the third anode is formed on the third p-type semiconductor layer.
24. The unit pixel of claim 23 , wherein the third active layer includes AlInGaP.