BIDIRECTIONAL LIGHT SHEET
A solid state light sheet and method of fabricating the sheet are disclosed. In one embodiment, bare LED chips have top and bottom electrodes, where the bottom electrode is a large reflective electrode. The bottom electrodes of an array of LEDs (e.g., greater than 1,000 LEDs) are bonded to an array of electrodes formed on a flexible bottom substrate. Conductive traces are formed on the bottom substrate connected to the electrodes. A transparent top substrate having conductors is then laminated over the bottom substrate. Various ways to connect the LEDs in series are described along with many embodiments. The light sheets may be formed to emit light from opposite surfaces of the light sheet, enabling it to be used in a hanging fixture to illuminate the ceiling as well as the floor.
1 . A bidirectional lighting device comprising:
a first plurality of non-packaged light emitting dies having electrodes;
wherein the light emitting dies each have a thickness less than 85 microns;
at least a first substrate and a second substrate sandwiching the light emitting dies and forming a light emitting structure having a first light emitting surface emitting light from the lighting device in a first direction and an opposing second light emitting surface emitting light from the lighting device in a second direction different from the first direction; and
conductors formed on the at least first substrate and second substrate electrically connected to the electrodes of the light emitting dies without wires for connecting the light emitting dies to a source of power.
2 . The device of claim 1 wherein,
the first substrate has first connection locations electrically connected to first conductors formed on the first substrate, wherein
each die has at least a first die electrode and a second die electrode, the first die electrode being formed on a primary light output surface of the die, wherein
some of the dies have their first die electrode aligned with and electrically connected to an associated one of the first connection locations on the first substrate without wire bonds, wherein
the second substrate has second connection locations electrically connected to second conductors formed on the second substrate, wherein
other ones of the dies have their first die electrode aligned with and electrically connected to an associated one of the second connection locations on the second substrate without wire bonds, and wherein
the first substrate and the second substrate have light output surfaces for emitting light in different directions from at least the primary light output surfaces of the dies.
3 . The device of claim 2 further comprising an intermediate layer between the first substrate and the second substrate.
4 . The device of claim 2 wherein the first substrate and the second substrate directly contact each other with no intermediate layer between them.
5 . The device of claim 2 wherein at least some of the dies are connected in series by the first conductors and the second conductors.
6 . The device of claim 5 wherein the at least some of the dies are connected in series by the first conductors and the second conductors interconnecting the first die electrodes to the second die electrodes.
7 . The device of claim 1 further comprising:
an intermediate layer over the first substrate, the intermediate layer having holes corresponding to locations of the dies on the first substrate such that the dies are surrounded by walls of an associated hole,
wherein the plurality of dies are sandwiched between the first substrate and the second substrate, with the intermediate layer there between, wherein portions of the first conductors and portions of the second conductors connect at least some of the dies in series without using wire bonds.
8 . The device of claim 1 further comprising at least third substrate sandwiched between the first substrate and the second substrate, the third substrate having a reflective layer for reflecting light out through the first substrate and the second substrate.
9 . The device of claim 8 wherein the third substrate has third conductors formed on its surface for interconnecting at least some of the dies in series.
10 . The device of claim 1 further comprising a reflective layer between the first substrate and the second substrate, wherein some of the dies are located between the reflective layer and a light output surface of the first substrate, and other ones of the dies are located between the reflective layer and a light output surface of the second substrate.
11 . The device of claim 1 wherein the device is formed as a light sheet.
12 . The device of claim 11 wherein the device is suspended from a ceiling so that the first light emitting surface faces the ceiling and the second light emitting surface faces away from the ceiling.
13 . The device of claim 1 wherein the device is a flexible light sheet having transparent opposing light emitting surfaces.
14 . The device of claim 1 wherein the dies are vertical light emitting diodes (LEDs).
15 . The device of claim 1 further comprising a wavelength conversion material provided on or in the device for converting light emitted from the dies to white light.
16 . The device of claim 1 wherein at least some of the dies are connected in series by the conductors internal to the device within outer boundaries of the first substrate and the second substrate.
17 . The device of claim 1 wherein the device is part of a 2×4 foot ceiling fixture.
18 . The device of claim 1 wherein the first substrate and the second substrate each have dimensions of approximately 2×4 feet.
19 . The device of claim 1 , wherein the light emitting dies comprises a top surface area less than 100×100 microns.
20 . The device of claim 1 , wherein the wherein the light emitting dies comprises from about 5 to about 500 micro LEDs are disposed per 1 cm 2 of planar area of the device.
21 . A lighting apparatus comprising:
(A) a bidirectional lighting device comprising:
a first plurality of non-packaged light emitting dies having electrodes;
wherein the light emitting dies each have a thickness less than 85 microns;
at least a first substrate and a second substrate sandwiching the light emitting dies and forming a light emitting structure having a first light emitting surface emitting light from the lighting device in a first direction and an opposing second light emitting surface emitting light from the lighting device in a second direction different from the first direction; and
conductors formed on the at least first substrate and second substrate electrically connected to the electrodes of the light emitting dies without wires for connecting the light emitting dies to a source of power; and
(B) an electrical interface, wherein the bidirectional lighting device is capable of being in electrical communication with the electrical interface.