Method of aligning light emitting element and method of fabricating display device
A method of aligning a light emitting element includes providing ink including light emitting elements on a substrate, a first electrode and a second electrode spaced apart from the first electrode being disposed on the substrate, applying a first alternating current (AC) voltage having a first frequency to the first electrode and the second electrode, and applying a second AC voltage having a second frequency different from the first frequency to the first electrode and the second electrode after applying the first AC voltage.
1 . A method of aligning a light emitting element, comprising:
providing ink including a plurality of light emitting elements on a substrate, a first electrode and a second electrode spaced apart from the first electrode being disposed on the substrate, wherein an insulating layer is disposed on the substrate and covers each of the first electrode and the second electrode;
performing first aligning operation of the light emitting element by applying a first alternating current (AC) voltage having a first frequency between the first electrode and the second electrode such that the plurality of light emitting elements are biased and aligned in a same direction; and
performing second aligning operation of the light emitting element by applying a second AC voltage having a second frequency different from the first frequency between the first electrode and the second electrode after the applying of the first AC voltage such that the plurality of light emitting elements are placed on the first electrode and the second electrode, wherein
the first frequency is a frequency in case that a real part of a Clausius-Mossotti (CM) factor is less than 0, and
the CM factor is defined as
f
CM
=
ℰ
𝓅
*
-
ℰ
m
*
ℰ
𝓅
*
+
2
ℰ
m
*
,
where ε* p denotes a complex dielectric constant of any one of the plurality of light emitting elements, and ε* m denotes a complex dielectric constant of a solvent included in the ink, and
the second frequency is a frequency in case that a real part of a Clausius-Mossotti (CM) factor is greater than 0,
during the first aligning operation,
the light emitting element is aligned in a floating state between the first electrode and the second electrode while maintaining a separation with respect to the insulating layer,
an electric field is formed by the first AC voltage having the first frequency, wherein the electric field is formed between the first electrode and the second electrode and around the light emitting element so that the light emitting element which is in the floating state acts as an induced dipole and an induced quasi-permanent dipole, and
in case that a magnitude of a repulsive force acting on the induced quasi-permanent dipole is greater than a magnitude of an attractive force acting on the induced dipole, the light emitting element which is in the floating state is biased and aligned in the same direction between the first electrode and the second electrode by a switching force acting on the induced quasi-permanent dipole, wherein the switching force changes a biased direction of the light emitting element to an opposite direction.
2 . The method according to claim 1 , wherein
each of the plurality of light emitting elements comprises a first conductive semiconductor and a second conductive semiconductor, and
the applying of the second AC voltage is performed after the plurality of light emitting elements are biased and aligned by the first AC voltage such that the first conductive semiconductor of each of the plurality of light emitting elements is oriented toward the first electrode and the second conductive semiconductor of each of the plurality of light emitting elements is oriented toward the second electrode.
3 . The method according to claim 2 , wherein the applying of the second AC voltage is performed before the plurality of light emitting elements are disposed on the first electrode and the second electrode.
4 . The method according to claim 1 , wherein the second frequency of the second AC voltage is greater than the first frequency of the first AC voltage.
5 . The method according to claim 1 , wherein each of the first AC voltage and the second AC voltage has an asymmetrical waveform.
6 . The method according to claim 1 , wherein a waveform of each of the first AC voltage and the second AC voltage includes at least one of a square waveform, and a triangular waveform.
7 . The method according to claim 1 , wherein the first AC voltage is a voltage obtained by adding a direct current (DC) offset voltage to a third AC voltage having the first frequency of the first AC voltage.
8 . A method of fabricating a display device, comprising:
disposing a first electrode and a second electrode spaced apart from the first electrode on a substrate, wherein an insulating layer is disposed on the substrate and covers each of the first electrode and the second electrode;
providing ink including a plurality of light emitting elements on the substrate; and
aligning the plurality of light emitting elements on the first electrode and the second electrode,
wherein the aligning of the plurality of light emitting elements on the first electrode and the second electrode comprises:
performing first aligning operation of the light emitting element by applying a first alternating current (AC) voltage having a first frequency between the first electrode and the second electrode such that the plurality of light emitting elements are biased and aligned in a same direction; and
performing second aligning operation of the light emitting element by applying a second AC voltage having a second frequency different from the first frequency between the first electrode and the second electrode after applying the first AC voltage such that the plurality of light emitting elements are placed on the first electrode and the second electrode,
wherein
the first frequency is a frequency in case that a real part of a Clausius-Mossotti (CM) factor is less than 0, and
the CM factor is defined as
f
CM
=
ℰ
𝓅
*
-
ℰ
m
*
ℰ
𝓅
*
+
2
ℰ
m
*
,
where ε* p denotes a complex dielectric constant of any one of the plurality of light emitting elements, and ε* m denotes a complex dielectric constant of a solvent included in the ink, and
the second frequency is a frequency in case that a real part of a Clausius-Mossotti (CM) factor is greater than 0,
during the first aligning operation,
the light emitting element is aligned in a floating state between the first electrode and the second electrode, while maintaining a separation with respect to the insulating layer,
an electric field is formed by the first AC voltage having the first frequency, wherein the electric field is formed between the first electrode and the second electrode and around the light emitting element so that the light emitting element which is in the floating state acts as an induced dipole and an induced quasi-permanent dipole, and
in case that a magnitude of a repulsive force acting on the induced quasi-permanent dipole is greater than a magnitude of an attractive force acting on the induced dipole, the light emitting element which is in the floating state is biased and aligned in the same direction between the first electrode and the second electrode by a switching force acting on the induced quasi-permanent dipole, wherein the switching force changes a biased direction of the light emitting element to an opposite direction.
9 . The method according to claim 8 , wherein
each of the plurality of light emitting elements comprises a first conductive semiconductor and a second conductive semiconductor, and
the applying of the second AC voltage is performed after the plurality of light emitting elements are biased and aligned by the first AC voltage such that the first conductive semiconductor of each of the plurality of light emitting elements is oriented toward the first electrode and the second conductive semiconductor of each of the plurality of light emitting elements is oriented toward the second electrode.
10 . The method according to claim 9 , wherein the applying of the second AC voltage is performed before the plurality of light emitting elements are disposed on the first electrode and the second electrode.
11 . The method according to claim 8 , wherein the second frequency of the second AC voltage is greater than the first frequency of the first AC voltage.
12 . The method according to claim 8 , wherein each of the first AC voltage and the second AC voltage has an asymmetrical waveform.
13 . The method according to claim 8 , wherein a waveform of each of the first AC voltage and the second AC voltage includes at least one of a square waveform, and a triangular waveform.
14 . The method according to claim 8 , wherein the first AC voltage is a voltage obtained by adding a direct current (DC) offset voltage to a third AC voltage having the first frequency of the first AC voltage.
15 . The method according to claim 1 , wherein the first AC voltage and the second AC voltage have a same waveform.
16 . The method according to claim 8 , wherein the first AC voltage and the second AC voltage have a same waveform.