T 1348/12 28-09-2017

1. The appeal is admissible.

2. The claimed invention

The application relates to GaN-based light emitting diodes (LEDs) having a vertical structure (see Figure 2). The LED comprises a first-type (n) GaN layer (140) and a second-type (p) GaN layer (180) with an active layer (160) between them. Under the first-type GaN layer there is a (first) electrode (500) and on top of the second-type GaN layer there is a (second) electrode (240). The first electrode (500) reflects the light emitted from the active layer so that most of the light is emitted through the top side (as seen in Figure 2) of the LED. On both electrodes there are metallic pads (500 and 260 in Figure 8) which are made of Au and have a thickness of at least 0.5 mym (see paragraphs [0026],[0027] and [0035] of the published application).

3. The closest prior art

3.1 The Examining Division regarded document D5 as the closest prior art. The Appellant did not contest this and the Board does not see any reason to differ.

D5 discloses a LED having a vertical structure (see Figure 1). The LED comprises several semiconductor layers (1) made of GaN (page 6, lines 34-36). Between these semiconductor layers there is an active layer (2) which generates the emitted light (page 7, lines 1-3). There is no explicit disclosure of p- and n-type GaN layers in D5, only of different semiconductor layers (page 6, line 36); it is, however, implicit that for the LED to function, the active layer must be placed between p-type and n-type semiconductor layers. There is a metallic surface (4) (at the bottom of the LED as seen in Figure 1), which is directly formed on the semiconductor layer and which functions as reflector (6) for the light emitted from the active layer (page 7, lines 5-11). This causes most of the generated light to be emitted from the top of the LED (as seen in Figure 1). This metallic surface serves also as a contact (first electrode), while on the other side of the LED (i. e. top side) there is a second contact (electrode - 12) which is directly formed on the semiconductor layer (page 7, lines 11-13). There is no disclosure of pads in the LED of D5.

4. Main request

4.1 Compared to the LED in D5, the LED defined in claim 1 of the Main request comprises the additional features relating to the first and second pads, i. e. that there is a first pad on which the first electrode lies, that there is a second pad on the second electrode, that the pads are made of Au, that the second pad has a thickness of 0,5 mym or higher, that the second pad contacts the second electrode and that the width of the first electrode is greater than a width of the second pad.

4.2 These differentiating features provide the technical effect of allowing electrical connection and flow of electrical current through the LED, while at the same time ensuring mechanical stability of the electrical connection. The technical problem for the skilled person starting from D5 would thus be, how to modify the LED of D5 in order to obtain this technical effect.

4.3 In D5, it is indicated that the bottom part (metallic surface 4 - see Figure 1) of the LED should be put on a metallic piece (body - Metallkörper) which would function both as a carrier (Träger) as well as electrical contact (page 7, lines 13-17).

4.4 Document D6 describes a LED having also a vertical structure and shows (Figure 2(d)) the use of metallic pads (bonding electrodes 6) on the electrodes (ohmic contacts 4 and 5; see also pages 6 and 8 of D6a) which are formed on either side of the LED.

4.5 The skilled person starting from D5 and trying to solve the identified technical problem, would find the obvious solution to add pads on the electrodes of the LED, as already hinted in D5 and indicated in D6. As described in D6, the pads are made of the same material (Au) and have the same thickness (5000A = 0.5 mym) as the ones in the claim (see page 8 D6a). It is considered self-evident that the second pad (i. e. the one on the top in Figure 1 of D5) would contact the second electrode. From Figure 1 of D5, it becomes also evident that the width of the first electrode (4) would be greater than the width of the second pad (which would be on the second electrode/contact (12)).

Hence, the subject matter of claim 1 of the Main request is obvious to the skilled person taking the combination of D5 and D6 into account.

4.6 The Appellant argued that the technical problem should not be formulated so broadly. LEDs made of GaN were a specific type of diodes with specific technology and corresponding problems. Therefore, the problem should be reformulated as how to allow electrical connection and flow of electrical current through a GaN-based LED, while at the same time ensuring mechanical stability. Faced with this technical problem, the skilled person starting from D5 (which also describes GaN-based LEDs) would never look into D6 for a solution because the LED in D6 comprised semiconductor layers made of SiC (see D6, abstract), which is a different material, with different properties and associated issues.

Even if the skilled person were to consider D6, the combination of the teachings of D5 and D6 would still not disclose the feature of the second pad contacting the second electrode that is electrically connected to the second-type GaN layer because in D6 the corresponding electrode was contacting a SiC layer and not a GaN layer.

4.6.1 The Board cannot follow the Appellant's argument. The use of pads on the electrodes of the LED is unrelated to the semiconductor material used. The pads are not connected to the semiconductor layers directly but to the electrodes (metallic contacts). Even if it were considered that GaN-based semiconductors are different from SiC-based semiconductors, this would be irrelevant to the use of the pads since the pads address a technical problem which is common in both types of LEDs: to allow electrical connection and flow of electrical current through the LED and to ensure mechanical stability of the electrical connection. Hence, the Board remains with the definition of the technical problem to be solved as it is formulated in paragraph 4.2 above.

In addition, since the contacts (electrodes) contacting the GaN layer are already part of the LED in D5, the skilled person would need only to take the pads from the LED of D6 and not any of the remaining layers. Hence, the combination of the two teaching will yield a LED with the features of claim 1.

4.7 The conclusion is that the subject matter of claim 1 of the Main request does not involve an inventive step within the meaning of Article 56 EPC 1973.

5. First Auxiliary Request

Claim 1 of the First Auxiliary request differs from Claim 1 of the Main request only in wording. As the Appellant also confirmed during the oral proceedings, the subject matter of the two claims is the same.

Consequently, Claim 1 of the First Auxiliary request does not involve an inventive step within the meaning of Article 56 EPC 1973 for the same reasons as for the Main request.

6. Second Auxiliary request

6.1 Claim 1 of the Second auxiliary request defines a light emitting diode with only one GaN layer, which is a p-GaN layer.

In the originally filed application, however, there is no embodiment of a LED without both a n-GaN (first-type) layer and a p-GaN (second-type) layer. Neither is there any indication that would lead the skilled person to derive such an embodiment in a direct and unambiguous manner.

6.2 Hence, the omission of the n-type GaN layer in the definition of the LED in claim 1 amounts to an intermediate generalisation, which has no basis in the originally filed application. The Appellant did not provide any comments on this objection by the Board, neither in writing nor during the oral proceedings.

6.3 The conclusion is, therefore, that claim 1 of the Second Auxiliary request does not meet the requirements of Article 123(2) EPC.