Method for fabricating integrated alternating-current light-emitting-diode module

A method for fabricating an integrated AC LED module comprises steps: forming a junction layer on a substrate, and defining a first growth area and a second growth area on the junction layer; respectively growing a Schottky diode and a LED on the first growth area and the second growth area; forming a passivation layer and a metallic layer on the Schottky diode, the LED and the substrate. Thereby, the Schottky diode is electrically connected with the LED via the metallic layer. Thus is promoted the reliability of electric connection of diodes, reduced the layout area of the module, and decreased the fabrication cost.

FIELD OF THE INVENTION

The present invention relates to an AC LED module, particularly to a method for fabricating an AC LED module through integrating Schottky diodes and LEDs.

BACKGROUND OF THE INVENTION

Because of durability, lightweight and power efficiency, LED (Light Emitting Diode) has been massively applied to various optoelectronic products, such as indicators, illuminators and displays. Traditionally, LED is driven by DC (Direct Current) power. However, the power source available in the daily life environment is AC (Alternating Current) power. Thus, LED needs to be driven by an AC-DC converter and a step-down transformer, which increase the fabrication cost. Further, energy is wasted when AC is converted into DC.

A U.S. Pat. No. 7,531,843 disclosed a LED structure with an AC circuit, wherein the opposite electrodes of at least two LEDs are connected in parallel, and wherein the LEDs are driven by AC to emit light alternatingly according to the electric connection thereof Such a design indeed makes LEDs able to emit light under AC. However, every LED chip can only emit light at one of the semi-cycles of AC. Thus, only one half of LEDs operate at any moment of AC application, and there are always another half of LEDs idle and wasted.

An R.O.C. Pub. No. 201104911 disclosed a LED illumination device, which integrates a plurality of LEDs and a plurality of rectifier elements (Schottky diodes) to form a Wheatstone bridge-like structure, whereby every LED emits light in the complete cycle of AC, whereby is increased the use rate of LEDs, and whereby is promoted uniformity of illumination. However, the LEDs and rectifier elements are integrated in a wire-bonding method, which not only raises the fabrication cost but also increases the layout area of the device. Besides, the wire-bonding process may decrease the reliability of the device.

A U.S. Pub. No. 20110059559 disclosed an AC light emitting device and a method for fabricating the same, wherein a plurality of light emitting elements are formed on a substrate, and wherein a rectifier-dedicated region is formed on the surface of a portion of the light emitting elements, and wherein rectifier elements are formed on the rectifier-dedicated region, and wherein at least four rectifier elements are arranged to form a Wheatstone bridge functioning as a rectification unit, whereby every LED emits light in the complete cycle of AC, and whereby the rectifier elements have higher inverse bias resistance and lower turn-on voltage. However, in the prior art, the rectifier-dedicated layer is fabricated on the light emitting elements with an epitaxial method or a deposition method after the light emitting element has been fabricated. Next, an etching method is used to define the rectifier elements and the light emitting elements. Such a fabrication process is likely to damage the surface of the light emitting elements, degrade the electric performance of the light emitting elements and lower the light efficiency of the light emitting elements.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to solve the conventional problem that the wire-bonding process for integrating rectifier elements and LEDs not only increases fabrication cost and layout area but also results in poor reliability.

Another objective of the present invention is to solve the conventional problem that the re-etch process is likely to damage the surface of LEDs and decrease the light efficiency of LEDs when the rectifier elements and LEDs are grown on an identical substrate.

To achieve the abovementioned objectives, the present invention proposes a method for fabricating an integrated AC LED module, which comprises steps:

providing a substrate and a junction layer on the substrate, wherein at least one first growth area, at least one second growth area, and at least one non-growth area between the first and second growth areas are defined on the surface of the junction layer;

respectively forming a Schottky diode and a LED on the first growth area and the second growth area, and respectively defining a first electric connection area and a second electric connection area on the Schottky diode and the LED;

removing the non-growth area of the junction layer until the substrate is exposed in order to separate the first growth area and the second growth area by a gap;

forming a passivation layer on a portion of the substrate, the Schottky diode and the LED, wherein the portion of the substrate is the area corresponding to the non-growth area, and wherein the first and second electric connection areas are exposed; and

forming a metallic layer on the passivation area, the first electric connection area and the second electric connection area so as to electrically connect the Schottky diode with the LED via the metallic layer.

In one embodiment, the Schottky diode is formed on the junction layer firstly in the step of forming the Schottky diode and the LED. Next, the Schottky diode respectively on the second growth area and the non-growth area is removed. Then, the LED is grown on the second growth area.

In another embodiment, the LED is formed on the junction layer firstly in the step of forming the Schottky diode and the LED. Next, the LED respectively on the first growth area and the non-growth area is removed. Then, the Schottky diode is grown on the first growth area.

The present invention respectively grows the Schottky diode and the LED on the first growth area and the second growth area, which are separated by a gap, to overcome the conventional problem of damaged LED surface and downgraded light efficiency resulting from using an etching process to separate the overlapped Schottky diode and LED. The present invention further forms a metallic layer to electrically connect the Schottky diode with the LED, whereby is decreased layout area, increased reliability of electric connection, and reduced fabrication cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The technical contents of the present invention are described in detail in cooperation with the drawings below.

Refer toFIG. 1andFIGS. 2A-2J.FIG. 1shows a flowchart of a method for fabricating an integrated AC LED module according to one embodiment of the present invention.FIGS. 2A-2Jare sectional views schematically showing the process to fabricate an integrated AC LED module according to one embodiment of the present invention. The present invention comprises the following steps.

Step S1: provide a substrate10and a junction layer11on the substrate10; define on the junction layer11at least one first growth area111, at least one second growth area112, and at least one non-growth area113between the first and second growth areas111and112.

Step S2: respectively grow Schottky diodes20and LEDs30on the first growth areas111and the second growth areas112; respectively define first electric connection areas21and second electric connection areas31on the surfaces of the Schottky diodes20and the LEDs30.

Step S3: remove the non-growth area113of the junction layer11until the substrate10is exposed, whereby the first growth area111and the second growth area112are separated by a gap d.

Step S4: form a passivation layer40on the Schottky diodes20, the LEDs30and the substrate10corresponding to the non-growth areas113with first electric connection areas21and the second electric connection areas31being exposed.

Step S5: form a metallic layer50on the passivation layer40, the first electric connection areas21and the second electric connection areas31, whereby the metallic layer50electrically connect the Schottky diodes20and the LEDs30.

Refer toFIGS. 2A-2Jsectional views schematically showing the process to fabricate an integrated AC LED module according to one embodiment of the present invention. As shown inFIG. 2A, grow a junction layer11on a substrate10, and define a first growth area111, a second growth area112and a non-growth area113on the junction layer11, wherein the non-growth area113is located between the first and second growth areas111and112. The substrate10is made of a material selected from a group consisting of sapphire, silicon, silicon carbide, and gallium nitride. The junction layer11is made of a material selected from a group consisting of gallium nitride, aluminum indium gallium nitride, and magnesium zinc oxide. In one embodiment, an N-type gallium nitride junction layer11is grown on a sapphire substrate10.

As shown inFIG. 2B, grow a Schottky diode20on the junction layer11by an MOCVD (Metalorganic Chemical Vapor Deposition) method. Next, use a photolithographic technology to etch off the Schottky diode20on the second growth area112until the junction layer11is exposed. The Schottky diode20includes a buffer layer22and an active layer23. The buffer layer22contacts the junction layer11and is located between the junction layer11and the active layer23. The buffer layer22is made of a material selected from a group consisting of gallium nitride, aluminum nitride, indium nitride, and combinations thereof. The active layer23is made of a material selected from a group consisting of gallium nitride, aluminum indium gallium nitride, and magnesium zinc oxide. In one embodiment, the Schottky diode20contains an aluminum gallium nitride/aluminum nitride dual-layer buffer layer22and a gallium nitride/aluminum gallium nitride/gallium nitride triple-layer active layer23.

As shown inFIG. 2CandFIG. 2D, form a first mask61over the non-growth area113and the Schottky diode20grown on the first growth area111. Next, selectively grow a LED30on the junction layer11with an MOCVD method. Next, remove the first mask61, whereby only the Schottky diode20and the LED30respectively remain on the first and second growth areas111and112of the junction layer11. In one embodiment, the LED30includes a P-type semiconductor layer32, an N-type semiconductor layer34, and an active layer33arranged between the P-type semiconductor layer32and N-type semiconductor layer34. The LED30is made of II-VI group and/or III-V group semiconductor materials. In one embodiment, the P-type semiconductor layer32is a multi-layer structure containing periodically stacked P-type gallium nitride and P-type aluminum gallium nitride; the active layer33is a quantum-well structure containing gallium nitride and indium gallium nitride; the N-type semiconductor layer34is a single-layer structure containing N-type gallium nitride.

As shown inFIG. 2E, deposit a second mask62on the surfaces of the Schottky diode20and the LED30with the non-growth area113being exposed to define the areas for the elements (i.e. the Schottky diode20and the LED30). Next, use a photolithographic technology to etch off the junction layer11below the non-growth area113and reveal the substrate10, whereby the diodes are separated by a gap and independent to each other. Next, remove the second mask62, whereby the first and second growth areas111and112of the junction layer11are separated by a gap d, as shown inFIG. 2F. It should be further explained that the region between two adjacent LEDs (not shown in the drawings) is also etched to reveal the substrate10and separate the two adjacent LEDs by another gap.

As shown inFIG. 2GandFIG. 2H, etch the LED30until the N-type semiconductor layer34is exposed. Next, use a photolithographic process to define a second electric connection area31on the LED30. The second electric connection area31includes an A connection area31aon the P-type semiconductor layer32and a B connection area31bon the N-type semiconductor area34. The Schottky diode20has a preset first electric connection area21. The first electric connection area21includes a C connection area21aand a D connection area21bseparated from the C connection area21aby a gap. As shown inFIG. 2H, sequentially vapor-deposit titanium, aluminum, titanium and gold on the C connection area21a, and fast anneal the metals into an alloy having lower ohmic contact resistance to obtain an ohmic electrode211. Next, form a passivation layer40on the Schottky diode20, the LED30and the substrate10corresponding to the non-growth area113. Next, use a photolithographic technology to etch off a portion of the passivation layer40but reveal the A connection area31a, the B connection area31b, the ohmic electrode211, and the D connection area21b, wherein the passivation layer40on the B connection area31bis etched to form a window312. In one embodiment, the passivation layer40is made of silicon dioxide.

As shown inFIG. 2I, vapor-deposit a conductive ITO (Indium Tin Oxide) film on the A connection area31ato form a P-type electrode311. In addition to ITO, the P-type electrode311may be made of a nickel-gold alloy, fluorine tin oxide, zinc aluminum oxide, or zinc gallium oxide. Next, vapor-deposit metals (including nickel and gold) on the D connection area21bto form a Schottky electrode212. The passivation layer40, the ohmic electrode211, the Schottky electrode212, and the P-type electrode311may also be fabricated in a different sequence, wherein the ohmic electrode211and the P-type electrode311are respectively formed on the C connection area21aand the A connection area31abeforehand. Next, grow the passivation layer40with the ohmic electrode211, the P-type electrode311, the D connection area21b, and the B connection area31bbeing exposed. Alternatively, the ohmic electrode211is formed on the C connection area21abeforehand. Next, grow the passivation layer40with the A connection area31abeing exposed. Then, the P-type electrode311is formed on the A connection area31a. And then, use a photolithographic technology to etch off a portion of the passivation layer40but reveal the D connection area21b, and the B connection area31b.

Next, grow the Schottky electrode212on the D connection area21b. Next, use a photolithographic technology to define the metal connection areas for cascading the diodes. As shown inFIG. 2J, vapor-deposit metals (including chromium and gold) to form a metallic layer50. Thus, the ohmic electrode211is electrically connected with the P-type electrode311via the metallic layer50, and the Schottky electrode212is electrically connected with the B connection area31bin the window312via the metallic layer50. Thereby, the Schottky diode20and the LED30are integrated to form an AC LED module.

In Step S2described above, the Schottky diode20is fabricated in advance, and the LED30is then fabricated succeedingly, as shown inFIGS. 2A-2F. Refer toFIGS. 3A-3Esectional views schematically showing the process to fabricate an integrated AC LED module according to another embodiment of the present invention, wherein the LED30is fabricated in advance, and then the Schottky diode20is fabricated succeedingly. Firstly, grow the LED30on the junction layer11. Next, use a photolithographic technology to etch off the LED30on the first growth area111and the non-growth area113until the junction layer11is exposed. Next, form a mask63on the non-growth area113and the surface of the LED30on the second growth area112. Next, grow the Schottky diode20. Next, remove the mask63. Thus, the Schottky diode20and the LED30are respectively formed on the first growth area111and the second growth area112.

In the embodiments described above, the Schottky diode20and the LED30are grown on the substrate10and electrically connected by the metallic layer50to form a Wheatstone bridge circuit. Refer toFIG. 4a diagram schematically showing an equivalent circuit according to one embodiment of the present invention. The equivalent circuit comprises a plurality of LEDs1and a plurality of Schottky diodes2, wherein the LEDs1and the Schottky diodes2are respectively equivalent to the LEDs30and the Schottky diodes20formed on the substrate10.

In conclusion, the present invention respectively grows the Schottky diode and the LED on the first growth area and the second growth area, which are separated from each other, to overcome the problem of the conventional technology that etches the overlapped LED and Schottky diode to form separate LED and Schottky diode and thus damages the surface of the LED and degrades the light efficiency of the LED. Further, the present invention uses a metallic layer to electrically connect the Schottky diode with the LED, whereby is reduced the layout area of the device, increased the reliability of the electric connection between elements, and reduced the fabrication cost.

The present invention indeed possesses utility, novelty and non-obviousness and meets the condition for a patent. Thus, the Inventors file the application for a patent. It is appreciated if the patent is approved fast.

The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the spirit of the present invention is to be also included within the scope of the present invention.