Optoelectronic light emitting device with a PWM transistor and method for manufacturing or controlling an optoelectronic light emitting device

Abstract

An optoelectronic light emitting device includes an optoelectronic semiconductor component configured to generate light, a current source configured to generate a current, and a PWM transistor driven by a pulse-width modulated signal. The PWM transistor enters a first state or a second state based on said pulse-width modulated signal. The PWN transistor is configured to supply the optoelectronic semiconductor component with the current generated by the current source in the first state and to decouple it from the current generated by the current source in the second state. The current source is manufactured by a first technology and the PWM transistor is manufactured by a second technology.

Claims

1. An optoelectronic light emitting device, with: an optoelectronic semiconductor component configured to generate light, a current source configured to generate a current, and a PWM transistor which is driven by a pulse-width-modulated signal, which enters a first state or a second state as a function of the pulse-width-modulated signal and is configured to supply the optoelectronic semiconductor component with the current generated by the current source in the first state and to decouple it from the current generated by the current source in the second state, wherein the current source is manufactured by a first technology and the PWM transistor is manufactured by a second technology, wherein the second technology has a higher charge carrier mobility than the first technology, and wherein the first technology is a TFT technology and the second technology is a c-Si technology.

2. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic semiconductor component, the current source and the PWM transistor are connected in series.

3. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic semiconductor component and the PWM transistor are connected in parallel.

4. The optoelectronic light emitting device according to claim 1, wherein the PWM transistor is an IC, in particular a μIC.

5. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic semiconductor component is a μLED.

6. The optoelectronic light emitting device according to claim 5, wherein the PWM transistor is integrated into the μLED.

7. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic light emitting device comprises a plurality of optoelectronic semiconductor components, each of which is associated with a current source and a PWM transistor driven by a pulse-width modulated signal, and wherein the optoelectronic semiconductor components are arranged in rows and columns and control inputs of the PWM transistors arranged in a row are connected to one another.

8. The optoelectronic light emitting device according to claim 1, wherein the current source comprises at least one first transistor for generating the current and a capacitor for controlling the at least one first transistor with the capacitor voltage.

9. The optoelectronic light emitting device according to claim 8, wherein the optoelectronic light emitting device comprises at least a second transistor for coupling the capacitor to a programming line.

10. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic semiconductor component and the PWM transistor are arranged in a first circuit line and a second circuit line is connected in parallel to the first circuit line, and wherein the second circuit line is configured such that the current generated by the current source flows through the second circuit line when the PWM transistor is in the second state.

11. The optoelectronic light emitting device according to claim 1, wherein the optoelectronic light emitting device comprises a control unit which is configured to drive the PWM transistor with the pulse-width modulated signal.

12. A display comprising one or more optoelectronic light emitting devices according to claim 1.

13. A method for controlling an optoelectronic light emitting device, wherein the optoelectronic light emitting device comprises an optoelectronic semiconductor component for generating light, a current source for generating current, and a PWM transistor, wherein the PWM transistor is driven with a pulse width modulated signal and the PWM transistor enters a first state or a second state depending on the pulse width modulated signal, wherein the PWM transistor supplies the optoelectronic semiconductor component with the current generated by the current source in the first state and decouples it from the current generated by the current source in the second state, wherein the current source is manufactured by a first technology and the PWM transistor is manufactured by a second technology, wherein the second technology has a higher charge carrier mobility than the first technology, and wherein the first technology is a TFT technology and the second technology is a c-Si technology.

14. A method for manufacturing an optoelectronic light emitting device, wherein the optoelectronic light emitting device comprises an optoelectronic semiconductor component for generating light, a current source for generating current, and a PWM transistor driven by a pulse width modulated signal, wherein the PWM transistor enters a first state or a second state depending on the pulse width modulated signal, and the PWM transistor is configured to supply the optoelectronic semiconductor component with the current generated by the current source in the first state and to decouple the optoelectronic semiconductor component from the current generated by the current source in the second state, wherein the current source is manufactured using a first technology and the PWM transistor is manufactured using a second technology, wherein the second technology has a higher charge carrier mobility than the first technology, and wherein the first technology is a TFT technology and the second technology is a c-Si technology.

Description

(1) In the following, embodiments of the invention are explained in more detail with reference to the accompanying drawings. In these schematically show:

(2) FIG. 1 a schematic circuit diagram of an optoelectronic light emitting device;

(3) FIG. 2 an illustration of a PWM signal;

(4) FIG. 3 a circuit diagram of a circuit for realizing an optoelectronic light emitting device;

(5) FIG. 4 an illustration of the time course of programming a cell and a PWM cycle;

(6) FIG. 5 illustrations of the current and voltage over an LED during a rising slope of a PWM pulse for an optoelectronic light emitting device manufactured with a TFT technology;

(7) FIG. 6 an illustration of the current through an LED during successive cycles for an optoelectronic light emitting device manufactured using a TFT technology;

(8) FIG. 7 illustrations of the current and voltage over an LED during a rising slope of a PWM pulse for an optoelectronic light emitting device with a c-Si PWM transistor;

(9) FIG. 8 an illustration of the current through an LED during successive cycles for an optoelectronic light emitting device with a c-Si PWM transistor;

(10) FIG. 9 a circuit diagram of a further circuit for realizing an optoelectronic light emitting device;

(11) FIG. 10 an illustration of the current through an LED during a rising slope of a PWM pulse for the optoelectronic light emitting device shown in FIG. 9;

(12) FIG. 11 an illustration of the current through the LED during successive cycles for the optoelectronic light emitting device shown in FIG. 9;

(13) FIG. 12 a circuit diagram of a further circuit for realizing an optoelectronic light emitting device with an LED;

(14) FIG. 13 a circuit diagram of a further circuit for realizing an optoelectronic light emitting device with multiple LEDs;

(15) FIG. 14 an illustration of the time course of the control of the optoelectronic light emitting devices according to FIGS. 12 and 13;

(16) FIGS. 15 to 19 illustration of variants of the circuit of FIG. 12;

(17) FIG. 20 different variants of a component with a μLED and a PWM transistor; and

(18) FIGS. 21 and 22 different variants of a circuit with an RGB trip LED.

(19) In the following detailed description, reference is made to the accompanying drawings, which form a part of this description and in which specific embodiments in which the invention may be practiced are shown for illustrative purposes. Since components of embodiments may be positioned in a number of different orientations, the directional terminology is for illustrative purposes and is not limiting in any way. It is understood that other embodiments may be used and structural or logical changes may be made without departing from the scope of protection. It is understood that the features of the various embodiments described herein may be combined with each other, unless specifically indicated otherwise. Therefore, the following detailed description is not to be construed in a limiting sense. In the figures, identical or similar elements are provided with identical reference signs where appropriate.

(20) FIG. 1 shows a schematic circuit diagram of an optoelectronic light emitting device 10. The optoelectronic light emitting device 10 contains an optoelectronic semiconductor component designed as an LED 11, in particular as a μLED, for generating light. The optoelectronic light emitting device 10 can furthermore contain further LEDs or μLED and can be integrated into a display.

(21) Further, the optoelectronic light emitting device 10 includes a controllable current source 12 for generating a current and a PWM transistor 13. The current source 12 and the PWM transistor 13 are controlled by a control unit 14.

(22) Data words 15 are input to an input of the control unit 14. The control unit 14 controls the current source 12 by means of a control signal 16 and the PWM transistor 13 by means of a control signal 17 in such a way that a data word 15 input into the control unit 14 is converted into a brightness value of the light generated by the LED 11.

(23) The control signal 17 for driving the PWM transistor 13 is a pulse-width modulated signal. The PWM transistor 13 enters a first state or a second state depending on the pulse width modulated signal. In the first state of the PWM transistor 13, the LED 11 is supplied with the current generated by the current source 12, while in the second state of the PWM transistor 13, the LED 11 is decoupled from the current generated by the current source 12, i.e., is not supplied with the current.

(24) In the present embodiment, the PWM transistor 13 is designed as a field effect transistor. The gate terminal of the PWM transistor 13 is driven by the control signal 17. The drain-source path of the PWM transistor 13 is connected between the LED 11 and the current source 12. In the first state of the PWM transistor 13, the drain-source path has a low impedance and in the second state it has a high impedance.

(25) Alternative circuits of the LED 11, the current source 12 and the PWM transistor 13 are described further below. In particular, the PWM transistor 13 can also be arranged in parallel with the LED 11.

(26) The current source 12 or the transistors included in the current source 12 are manufactured using a first technology, while the PWM transistor is manufactured using a second technology that has a higher carrier mobility than the first technology.

(27) As an example, a control signal 17 plotted against time t, i.e. a pulse width modulated signal applied to the gate terminal of the PWM transistor, is shown in FIG. 2. The control signal 17 can enter two discrete values, i.e. a first value 18 and a second value 19. During the period in which the control signal 17 enters the first value 18, a rectangular pulse with a pulse width t.sub.1 is generated. The pulse is repeated periodically with a period length T. When the control signal 17 enters the first value 18, i.e. during the duration t.sub.1 of the pulse, the drain-source path of the PWM transistor 13 is of low resistance. Otherwise, the drain-source path is high-impedance. In particular, the control unit 14 can control the pulse width t.sub.1 of the pulse.

(28) FIG. 3 shows a schematic circuit diagram of a circuit 20 which can be used to realize the optoelectronic light emitting device 10 shown in FIG. 1. The circuit 20 is used to drive the LED 11. Of course, further LEDs can be provided, arranged in rows and columns, for example, and driven by means of analog circuits.

(29) The circuit 10 comprises a controllable current source formed as a 3T1C cell having three transistors 21, 22, 23 formed as field effect transistors and a capacitor 24. Furthermore, the circuit 20 comprises the PWM transistor 13. The circuit 20 may therefore also be referred to as a 4T1C cell.

(30) The current-carrying paths, i.e. the drain-source paths, of the transistors 21, 22, 23 are connected in parallel. The LED 11, the drain-source path of the PWM transistor 13 and the transistor group consisting of the transistors 21, 22, 23 are connected in series.

(31) In the present embodiment, a supply potential VDD is applied to the anode terminal of the LED 11.

(32) The gate terminal of the PWM transistor 13 is driven by a signal S1.

(33) A first terminal of the capacitor 24 is connected to the gate terminals of the transistors 21, 22, 23. A second terminal of the capacitor 24 is connected to a ground potential GND.

(34) Furthermore, the circuit 20 comprises transistors 25, 26. The transistors 25, 26 are each connected with one terminal of their drain-source paths between the transistors 21, 22, 23 and the PWM transistor 13. The other terminal of the drain-source path of transistor 26 is connected to a programming line and has a signal sense applied to it. The other terminal of the drain-source path of transistor 25 is connected to the first terminal of capacitor 24.

(35) The gate terminals of transistors 25, 26 are driven by a signal ProgEn.

(36) In FIG. 3, two different areas 27, 28 of the circuit 20 are indicated by dashed lines. Area 27 was manufactured using the first technology and area 28 was manufactured using the second technology. In the present embodiment, the first technology is a TFT technology and the second technology is a c-Si technology. Consequently, the transistors 21, 22, 23, 25, 26 are thin film transistors (TFTs). The PWM transistor 13 is made of crystalline silicon. For example, the PWM transistor 13 may be a μIC. The PWM transistor 13 may further be manufactured as a printable μ-transistor or may be locally manufactured as a recrystallized single transistor using a laser beam.

(37) In circuit 20, the actual current driver consists of transistors 21, 22, 23. When in the ProgEn=VDD and S1=GND state, the drain-source paths of transistors 25, 26 are low impedance and the drain-source path of PWM transistor 13 is high impedance, a current can be impressed across the programming line which, since PWM transistor 13 is closed, charges or programmes the transistor 24 and produces exactly the gate-source voltage on the transistor network of transistors 21, 22, 23 necessary to drive the desired rated current.

(38) If in the state ProgEn=GND and S1=VDD the drain-source paths of the transistors 25, 26 are high impedance and the drain-source path of the transistor 13 is low impedance, the corresponding current flows through the LED 11, which is specified by the voltage of the capacitor 24. This can be modulated via the signal S1 driving the PWM transistor 13 in the sense of a PWM.

(39) In FIG. 4 the signals S1 and ProgEn as well as the current I.sub.LED flowing through the LED 11 are plotted against time t. First, the state ProgEn=VDD and S1=GND is switched to allow the cell or capacitor 24 to be programmed. Then, the PWM cycle is performed with ProgEn at GND and the PWM signal S1 driving the PWM transistor 13 with a predetermined pulse width.

(40) FIGS. 5 and 6 show measured curved for circuit 20, and in this case both areas 27 and 28 were manufactured using TFT technology. In FIG. 5, the current I.sub.LED and voltage V.sub.LED across LED 11 are shown during a rising slope of a PWM pulse. The maximum rise time, i.e., the time between the two dashed lines shown in FIG. 5, is about 10 ns, which shows that the circuit 20 is generally suitable for PWM dimming.

(41) FIG. 6 shows the decrease in current I.sub.LED due to switching of PWM transistor 13 during successive cycles. The reason for the decrease in current I.sub.LED is the injection of charge into capacitor 24 with each PWM pulse. However, the current I.sub.LED decreases only slightly over the 500 cycles shown during which capacitor 24 is not recharged. Consequently, the effect of the switching pulses in the load path on the charge of capacitor 24 can be neglected.

(42) For the curves shown in FIGS. 7 and 8, respectively, the same measurements were made as for FIGS. 5 and 6, respectively, but in this case region 27 of circuit 20 was manufactured using TFT technology, while region 28 was manufactured using c-Si technology.

(43) FIG. 7 shows that the rise time has been significantly reduced by making the PWM transistor 13 from crystalline silicon. The maximum rise time is now only about 5 ns. Furthermore, there is almost no change in the current I.sub.LED over several cycles, as FIG. 8 shows.

(44) FIG. 9 shows a schematic diagram of a circuit 30 based on the circuit 20 shown in FIG. 3.

(45) The portion 28 of the circuit 30 manufactured using the second technology includes a first circuit line 31 and a second circuit line 32 connected in parallel with the first circuit line 31. The first circuit line 31 comprises the LED 11 and the PWM transistor 13.

(46) The second circuit line 32 includes a pn diode 33 and transistors 34, 35 formed as field effect transistors. The drain-source paths of transistors 34, 35 are connected in series with the pn diode 33. The gate terminal of transistor 34 is driven by signal S1. The gate terminal of transistor 35 is driven by signal ProgEn.

(47) Transistors 34, 35 are designed as p-channel transistors, whereas transistors 13, 25, 26 are designed as n-channel transistors.

(48) The current generated by transistors 21, 22, 23 flows through the second circuit line 32 when the drain-source path of PWM transistor 13 is at high impedance.

(49) FIG. 10 shows, analogously to FIG. 7, the current I.sub.LED through LED 11 of circuit 30 during a rising slope of a PWM pulse. The maximum rise time, i.e. the time between the two dashed lines shown in FIG. 10, is only about 2 ns.

(50) FIG. 11 shows the magnitude of current I.sub.LED during successive cycles for circuit 30. The change in current I.sub.LED is very small.

(51) FIG. 12 shows a schematic circuit diagram of a circuit 40, which is a simplified variant of circuit 20. Circuit 40 contains only transistor 21 as the current-driving transistor. The capacitor 24 is programmed via the transistor 25. Furthermore, the PWM transistor 13 manufactured by means of c-Si technology is connected between the supply potential VDD and the LED 11.

(52) FIG. 13 shows several LEDs 11 arranged in one row of a display, each of which is driven by the circuit 40 known from FIG. 12. The gate terminals of the PWM transistors 13 arranged in the same row are connected to each other and are driven by the signal S1. Furthermore, the gate terminals of the transistors 25 arranged in the same row are driven by the signal ProgEn.

(53) FIG. 14 shows the timing of the control. The top row of FIG. 14 shows the signal S1 applied to the gate terminals of the PWM transistors 13. The middle row of FIG. 14 shows the gate-source voltage V.sub.GS of one of the transistors 21, and the bottom row of FIG. 14 shows the signal ProgEn applied to the gate terminals of the transistors 25.

(54) To program the capacitors 24, the signal ProgEn is switched on so that the drain-source paths of the transistors 25 are low impedance and the capacitors 24 can be charged to a respective voltage by means of the signals Sense 1, Sense 2, . . . Sense n can be charged to a respective voltage. As a result, the desired gate-source voltages V.sub.GS are generated at the transistors 21. These voltages subsequently define the current I.sub.LED through the respective LED 11.

(55) After programming the capacitors 24, the pulse width modulated signal S1 is applied to the gate terminals of the PWM transistors 13. The pulse-width modulated signal S1 only switches the current I.sub.LED through the respective LED 11 on and off.

(56) The row synchronous signal S1 serves as global dimming signal. Grayscale and calibration are realized by the TFT part, which can also be called slow PWM (compared to fast PWM by means of the PWM transistors 13).

(57) An alternative solution with a switching of the entire voltage V.sub.LED via the LEDs 11 is not preferred for power stability reasons.

(58) In contrast, the switching of the PWM transistors 13 requires only a few μA and can therefore also be implemented row-parallel to the switching of the gate signal ProgEn without any problems.

(59) If the row-synchronous signal S1 is used as a global dimming signal, the signal S1 can be shifted to the respective next line with a shift register analog to the signal ProgEn. This can be realized with only little effort.

(60) Since the signal S1 only has an on/off task, i.e. it does not control the current I.sub.LED, no complex designs regarding temperature, drift or other compensations are necessary here. Consequently, only the PWM transistor 13 has to switch at high speed between an on and an off state.

(61) FIG. 13 shows a so-called common anode arrangement in which the supply potential VDD is applied to the anode terminals of the LEDs 11. Alternatively, the LEDs 11 can also be arranged in a so-called common cathode arrangement, in which the cathode terminals of the LEDs 11 are connected to the ground potential GND.

(62) FIGS. 15 to 19 show variants of the circuit 40 shown in FIG. 12.

(63) In the circuits 41 and 42 shown in FIGS. 15 and 16, respectively, the fast PWM transistor 13 is connected in parallel with the LED 11, with the circuits in FIGS. 15 and 16 being designed in form of a common cathode arrangement and a common anode arrangement, respectively. Instead of interrupting the current I.sub.LED through the LED 11, the current I.sub.LED is short-circuited by the PWM transistor 13 in FIGS. 15 and 16. Thus, the slower TFT transistor 21, which is designed as PMOS in FIG. 15 or as NMOS in FIG. 16, is not significantly involved in the modulation of the LED cross current. Only the change in the transverse current caused by the rapid change in the voltage V.sub.DS of transistor 21, motivated by the finite internal resistance of the current source mapped by transistor 21, must be borne by the slower transistor.

(64) However, in case of circuits 41, 42 the maximum LED current is drawn for a longer time even with small pulse widths. To reduce the current consumption, the slow TFT transistor 21 can be switched off after short-circuiting the LED 11.

(65) The circuit shown in FIG. 17 differs from the circuit shown in FIG. 12 in that the PWM transistor 13 is arranged between the transistor 21 and the ground potential GND.

(66) In FIGS. 18 and 19, one terminal of the capacitor 24 has the supply potential VDD applied to it. Furthermore, in FIG. 18, the LED 11 is arranged between the transistor 21 and the PWM transistor 13. In FIG. 19, the transistor 21 is arranged between the PWM transistor 13 and the LED 11, and the cathode of the LED 11 has the ground potential GND applied to it.

(67) An advantage of the circuits described above is that a large part of the respective circuit can be realized in traditional TFT electronics, e.g. IGZO or LTPS. This includes, among other things, current dimming, e.g. 7 bits, and additionally a simple PWM, e.g. 8 bits with e.g. >1 μs shortest LTPS pulse width.

(68) Higher-level fast PWM with ultra-short pulses, e.g. 10 ns, is achieved by c-Si, i.e. crystalline silicon. The fast PWM can be achieved e.g. by a Si-(μ)chip, i.e. a hybrid concept, or by locally generated crystalline silicon, e.g. by laser recrystallization. Since the “fast” part of the circuit is spatially very limited (e.g., only a simple on/off FET in the simplest case), the additional cost (silicon area) is kept within limits. In addition, an external dimmer (combination TFT+ext. dimmer) can be dispensed with. Among other things, this saves component height or display height and increases efficiency.

(69) The PWM transistor 13 can already be integrated in the μLED and in this case is supplied by the “μLED component”. This reduces e.g. the costs for the external placing/printing of e.g. μ-transistors or the additional recrystallization of a TFT transistor. This is technologically possible for all three colors red, green and blue. Since both GaAs and GaN have high charge carrier mobilities, fast PWM can be realized as a result. Since the PWM transistor 13 has a pure on/off functionality, the requirements are low.

(70) The switching functionality can also be integrated into a sub-mount, carrier or interposer of the LED. It is conceivable here to mount RGB trip LEDs on an interposer, for example, which contains the PWM transistor. This is advantageous because the PWM transistor has approximately the same geometry as the (μ)LED and thus no additional area is consumed. Furthermore, only one additional pin or connection is required for the common PWM gate, for example.

(71) FIG. 20 shows three different variants in which the PWM transistor 13 is integrated in the μLED. In one variant, the PWM transistor 13 is arranged in parallel to the LED 11. In the other two variants, the drain-source path of the PWM transistor 13 is connected to the cathode or anode of the PWM transistor 13. Each of the components shown in FIG. 20 contains 3 connection pins.

(72) If the c-Si PWM transistor 13 is implemented as a μIC, several PWM switches can also be accommodated in one μIC. If, for example, 1 μIC is designed for 4 RGB pixels (12 LEDs), this μIC has “only” e.g. one PWM switch signal pad, 12 source or drain pads and one VDD or GND pad, i.e. a total of e.g. 18 pads. Due to its simplicity, the system can also be scaled to e.g. 16 pixels. Since only 1 transistor is required per LED, for example, high pixel densities can also be realized.

(73) FIG. 21 shows the circuit known from FIG. 13, where three LEDs 11 with the colors red, green and blue together with the associated PWM transistors 13 are integrated in a common substrate as an RGB trip LED, e.g. printable. The component 45 shown in FIG. 21 with the three LEDs 11 and the three PWM transistors 13 has, for example, at least 5 connections.

(74) 30

(75) FIG. 22 shows a circuit with three LEDs 11 of the colors red, green and blue. The drive circuits of the LEDs 11 correspond to the circuit in FIG. 16. Alternatively, the drive circuits can also be designed as a common cathode arrangement. The three LEDs 11 and the associated PWM transistors 13 can be integrated in a common substrate as an RGB trip LED. In FIG. 22, areas 46A, 46B, 46C are marked that are encompassed by the common substrate. For clarity, areas 46A, 46B, 46C are shown separately.

LIST OF REFERENCE SIGNS

(76) 10 optoelectronic light emitting device

(77) 11 LED

(78) 12 current source

(79) 13 PWM transistor

(80) 14 control unit

(81) 15 data word

(82) 16 control signal

(83) 17 control signal

(84) 18 first value

(85) 19 second value

(86) 20 circuit

(87) 21 transistor

(88) 22 transistor

(89) 23 transistor

(90) 24 capacitor

(91) 25 transistor

(92) 26 transistor

(93) 27 area

(94) 28 area

(95) 30 circuit

(96) 31 first circuit line

(97) 32 second circuit line

(98) 33 pn diode

(99) 34 transistor

(100) 35 transistor

(101) 40 circuit

(102) 41 circuit

(103) 42 circuit

(104) 45 component

(105) 46A area

(106) 46B area

(107) 46C area