CN112837651A

CN112837651A - Pixel driving circuit and display panel

Info

Publication number: CN112837651A
Application number: CN202110268249.0A
Authority: CN
Inventors: 胡晓斌
Original assignee: Shenzhen China Star Optoelectronics Semiconductor Display Technology Co Ltd
Current assignee: Shenzhen China Star Optoelectronics Semiconductor Display Technology Co Ltd
Priority date: 2021-03-12
Filing date: 2021-03-12
Publication date: 2021-05-25

Abstract

The application discloses a pixel driving circuit and a display panel, wherein the pixel driving circuit comprises a writing transistor and a driving transistor; the writing transistor is provided with a first grid and a second grid, and the first grid is connected with the second grid; the driving transistor has a third gate and a fourth gate, and the other of the source/drain of the writing transistor is connected to the third gate and the fourth gate. By adopting the writing transistor and the driving transistor with double gates, and the corresponding double gates are mutually connected, the driving voltage of the writing transistor and the driving transistor can be obviously reduced, and the luminous brightness of the pixel can be improved with lower power consumption and heat productivity.

Description

Pixel driving circuit and display panel

Technical Field

The application relates to the technical field of display, in particular to a pixel driving circuit and a display panel.

Background

LEDs based on Thin Film Transistor (TFT) backplane technology have shown to gain widespread attention in recent years. Unlike a voltage-driven TFT-LCD (Liquid Crystal Display), the TFT-LED Display requires current-driven light emission. This requires the pixel driving circuit to have a strong current driving capability. Therefore, the amorphous silicon (a-Si) based backplane technology is not suitable for high-density display such as AMOLED (Active Matrix organic light-Emitting Diode) because the channel material has low carrier mobility and weak current driving capability, and requires a large-sized TFT to provide sufficient current, which is not favorable for improving the resolution. The mobility of Low Temperature Polysilicon (LTPS) is significantly higher than that of IGZO (indium gallium zinc oxide) and a-Si, but the process is complicated, the uniformity is poor, the substrate size is small, and the LTPS is not suitable for large-sized display products. The mobility of IGZO is between A-Si and LTPS, the manufacturing process is relatively simple, and the current IGZO generation line is higher, so that the method is more suitable for manufacturing the large-size LED display driving back plate.

In the pixel driving circuit, in order to obtain a large driving current, the driving voltage of the IGZO type TFT is generally high, the on-state voltage of the gate electrode is generally 20V or more, and the off-state voltage is generally about-10V. Therefore, when the LED pixel driving circuit based on the IGZO backboard technology works, the voltage switching range of the driving signal is large. This aspect results in large dynamic power consumption, severe heat generation and long rise and fall time of the signal; on the other hand, the voltage stress level of the TFT device is increased, so that the aging of the device is accelerated; in addition, the risk of electrical breakdown at the crossover of the signal lines on the backplane is also increased.

Such as the pixel driving circuit shown in fig. 1, which includes a first transistor T1, a second transistor T2, a storage capacitor Cst, and a light emitting device LED. One of a source/drain of the first transistor T1 is for receiving a Data signal Data, a gate of the first transistor T1 is for receiving a Scan signal Scan, the other of the source/drain of the first transistor T1 is connected to a first end of the storage capacitor Cst and a gate of the second transistor T2, a second end of the storage capacitor Cst is connected to one of an anode of the light emitting device LED and a source/drain of the second transistor T2, a cathode of the light emitting device LED is connected to a constant voltage low potential signal VSS, and the other of the source/drain of the second transistor T2 is connected to a constant voltage high potential signal VDD.

The working principle is as follows: when the Scan signal Scan of a row of sub-pixels is at a high potential, the first transistor T1 is turned on, and the Data signal Data charges the gate (node G in fig. 1) of the second transistor T2 to a high potential; then, the Scan signal Scan changes to a low potential, the first transistor T1 is turned off, the potential of the point G maintains the charged potential, and the second transistor T2 is controlled to be turned on, at which time, a current flows through the light emitting device LED, and the light emitting device LED starts emitting light. In order to increase the light emission luminance, the size of the second transistor T2 needs to be increased, but this increases the space occupied by a single sub-pixel, which is not favorable for increasing the resolution; the driving voltage of the second transistor can also be increased, but this can lead to the problems described above.

Disclosure of Invention

Based on this, the application provides a pixel drive circuit and display panel, has solved the improvement of the luminance of pixel and has required great drive voltage, the high power consumption that leads to, high fever problem.

In a first aspect, the present application provides a pixel driving circuit comprising a write transistor and a drive transistor; the writing transistor is provided with a first grid and a second grid, and the first grid is connected with the second grid; the driving transistor has a third gate and a fourth gate, and one of the source/drain of the writing transistor is connected to the third gate and the fourth gate.

Based on the first aspect, in a first implementation manner of the first aspect, the pixel driving circuit further comprises a storage unit; one end of the memory cell is connected to the third gate, and the other end of the memory cell is connected to one of the source/drain of the driving transistor.

In a second implementation manner of the first aspect, based on the first implementation manner of the first aspect, the pixel driving circuit further comprises a light emitting unit; the first end of the light-emitting unit is connected with one of the source electrode and the drain electrode of the driving transistor, and the second end of the light-emitting unit is used for connecting a first power supply signal.

In a third implementation form of the first aspect, based on the second implementation form of the first aspect, the other of the source/drain of the driving transistor is used for accessing the second power supply signal.

Based on the third implementation manner of the first aspect, in the fourth implementation manner of the first aspect, the potential of the first power supply signal is lower than the potential of the second power supply signal.

In a fifth implementation form of the first aspect, the storage unit comprises a storage capacitor; one end of the storage capacitor is connected to the third gate, and the other end of the storage capacitor is connected to one of the source/drain of the driving transistor.

In a sixth implementation form of the first aspect, based on the fifth implementation form of the first aspect, the light emitting unit comprises a light emitting device; an anode of the light emitting device is connected to one of the source/drain electrodes of the driving transistor, and a cathode of the light emitting device is connected to the first power signal.

In a seventh implementation form of the first aspect based on any of the implementation forms described above, the channel type of the writing transistor is different from that of the driving transistor; and the writing transistor is a P-channel type thin film transistor.

In an eighth implementation form of the first aspect as any of the implementation forms above, the channel material of the writing transistor and the channel material of the driving transistor are the same; and the channel material of the driving transistor includes at least one of indium, gallium, and zinc.

In a second aspect, the present application provides a display panel including the pixel driving circuit in any of the above embodiments.

According to the pixel driving circuit and the display panel, the writing transistor and the driving transistor with the double grids are adopted, and the corresponding double grids are mutually connected, so that the driving voltage of the writing transistor and the driving transistor can be remarkably reduced, and the light emitting brightness of the pixel can be improved with low power consumption and low heat productivity.

Drawings

The technical solution and other advantages of the present application will become apparent from the detailed description of the embodiments of the present application with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of a pixel driving circuit in a conventional technical solution.

Fig. 2 is a schematic structural diagram of a pixel driving circuit according to an embodiment of the present disclosure.

Fig. 3 is a schematic structural diagram of a dual-gate transistor according to an embodiment of the present disclosure.

Fig. 4 is a schematic diagram showing the corresponding change of the threshold voltage and the potential of the sub-gate of the dual-gate transistor in fig. 3.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Referring to fig. 2 to 4, in fig. 2, the present embodiment provides a pixel driving circuit, which includes a writing transistor T1 and a driving transistor T2; the writing transistor T1 has a first gate and a second gate, the first gate and the second gate are used for accessing the Scan signal Scan, and one of the source/drain of the writing transistor T1 is used for accessing the Data signal Data; the driving transistor T2 has a third gate and a fourth gate, and the other of the source/drain of the writing transistor T1 is connected to the third gate and the fourth gate.

It is to be understood that, in the present embodiment, such a configuration of the writing transistor T1 and the driving transistor T2 can be applied to various pixel circuits or pixel driving circuits, which is not limited to the specific limitations of the pixel driving circuits provided in the present application.

It can be understood that, in the present embodiment, by using the writing transistor T1 and the driving transistor T2 with dual gates, and connecting the first gate to the second gate, and connecting the third gate to the fourth gate, the dual gates are connected to each other, so as to significantly reduce the driving voltages of the writing transistor T1 and the driving transistor T2, and further improve the light emitting brightness of the pixel with lower power consumption and heat generation.

Specifically, the first gate and the second gate of the write transistor T1 are both connected to the Scan signal Scan, and the turn-on voltage of the write transistor T1 is a negative value when the Scan signal Scan is at a high potential, so that a lower potential of the Scan signal Scan can ensure that the Data signal Data is written to the point G without distortion; meanwhile, when the Scan signal Scan is at a low potential, the threshold voltage of the write transistor T1 becomes large, and the Scan signal Scan low potential does not need to be too low, so that the write transistor T1 can be guaranteed to be completely turned off, and the leakage current is low. Therefore, the difference between the high and low voltages of the Scan signal Scan can be effectively reduced compared to the conventional three-terminal transistor-based driving circuit. The third gate and the fourth gate of the driving transistor T2 are also connected to each other, so that the threshold voltage of the driving transistor T2 is reduced to a negative value when the Data signal Data is at a high potential, and the Data signal Data, the first power signal VSS and the second power signal VDD are at the same voltage, and the current of the driving transistor T2 is larger in this embodiment.

As shown in fig. 3, the structure of the writing transistor T1 or the driving transistor T2 may be a double gate transistor having a main gate G1 and a sub-gate G2, which can control the on state of the transistors, and a drain D and a source S, on both upper and lower sides of an active layer.

As shown in fig. 3 and 4, in the dual-gate transistor, the potential of the sub-gate G2 can effectively control the threshold voltage Vth of the transistor, as shown in fig. 4. When the potential of the sub-gate G2 is low, for example, -10V, the threshold voltage Vth of the transistor is high, corresponding to 6V, and the transistor is turned off more easily in this state, and the leakage current is suppressed to a low level. When the voltage level of the sub-gate G2 is higher, for example, 15V, the turn-on voltage of the transistor is lower, corresponding to-4V, and the on-state current is larger, so that the voltage required to achieve the same on-state current can be lower compared to the conventional three-terminal transistor. Therefore, the off-state voltage can be increased while ensuring that the leakage current is low, for example, the off-state voltage ranges from-10V to-6V, and the on-state voltage (for example, 25V to 15V) can be reduced while ensuring that the on-state current of the double-gate transistor is large. Therefore, the voltage difference between the high potential and the low potential of the driving voltage in the pixel driving circuit can be reduced, and the effect of reducing the driving voltage is achieved.

In one embodiment, the pixel driving circuit further comprises a storage unit; one end of the memory cell is connected to the third gate, and the other end of the memory cell is connected to one of the source/drain of the driving transistor T2.

In one embodiment, the storage unit includes a storage capacitor Cst; one end of the storage capacitor Cst is connected to the third gate electrode, and the other end of the storage capacitor Cst is connected to one of the source/drain electrodes of the driving transistor T2.

In one embodiment, the pixel driving circuit further includes a light emitting unit; a first terminal of the light emitting unit is connected to one of the source/drain of the driving transistor T2, and a second terminal of the light emitting unit is used for receiving a first power signal VSS.

In one embodiment, the light emitting unit includes a light emitting device LED; an anode of the light emitting device LED is connected to one of the source/drain electrodes of the driving transistor T2, and a cathode of the light emitting device LED is connected to the first power signal VSS.

The light emitting device LED may be but not limited to an OLED, a Micro-LED, a Mini-LED or an LED.

In one embodiment, the other of the source/drain of the driving transistor T2 is used for accessing the second power signal VDD.

In one embodiment, the first power signal VSS is lower in potential than the second power signal VDD.

In one embodiment, the write transistor T1 is of a different channel type than the drive transistor T2; the writing transistor T1 may be, but not limited to, a P-channel type thin film transistor, and may alternatively be an N-channel type thin film transistor.

In one embodiment, the channel type of the writing transistor T1 is the same as that of the driving transistor T2, which can reduce the process complexity of manufacturing the pixel driving circuit.

In one embodiment, the channel material of the write transistor T1 and the drive transistor T2 are the same; and the channel material of the driving transistor T2 includes at least one of indium, gallium, and zinc. Wherein the channel material may be an oxide or a metal oxide.

In the pixel driving circuit, the pixel driving circuit includes: the first power signal VSS is a dc low potential, the second power signal VDD is a dc high potential, the Scan signal Scan is an ac signal or a square wave signal, the Scan signal Scan controls the writing transistor T1 to be turned on and off, and the Data signal Data is charged to the node G through the writing transistor T1, thereby controlling the driving transistor T2 to be turned on and off, and further controlling the light emitting device LED to emit light.

In one embodiment, the present application provides a display panel including the pixel driving circuit in any one of the above embodiments.

The display panel may be, but is not limited to, an OLED display panel, which is a display panel made using organic electroluminescent light emitting diodes. The organic electroluminescent diode has the advantages of no need of backlight source, high contrast, thin thickness, wide viewing angle, fast reaction speed, wide application temperature range, simple structure and manufacture process, etc. and is considered as a new application technology of the next generation of flat panel display.

Organic Light Emitting Diode (OLED) displays are becoming more common and are most prominent in products such as mobile phones, media players, and small entry-level televisions. Unlike standard liquid crystal displays, OLED pixels are driven by current sources. To understand how and why the OLED power supply affects the display quality, the OLED display technology and power supply requirements must be understood first. The latest OLED display technologies will be described herein, with major power supply requirements and solutions being discussed, and with the innovative power supply architecture specifically proposed for OLED power supply requirements also being introduced.

The backplane technology creates a flexible display: high resolution color Active Matrix Organic Light Emitting Diode (AMOLED) displays require the use of an active matrix backplane that uses active switching for switching each pixel. Liquid Crystal (LC) displays are well-established in amorphous silicon manufacturing, can be supplied with low-cost active matrix backplanes, and can be used in OLEDs. Many companies are developing Organic Thin Film Transistor (OTFT) backplane processes for flexible displays, which can also be used for OLED displays to realize the launch of full color flexible displays. Either standard or soft OLEDs require the same power supply and driving techniques. To understand OLED technology, function, and its interaction with the power supply, the technology itself must be thoroughly analyzed. OLED displays are a self-illuminating display technology that does not require any backlighting at all. The OLED is made of organic materials with applicable chemical structures. OLED technology requires a current-controlled driving method-OLEDs have electrical characteristics that are quite similar to standard Light Emitting Diodes (LEDs), with brightness all depending on the LED current. To turn on and off the OLED and control the OLED current, a control circuit using a Thin Film Transistor (TFT) is required.

The advanced power-save mode achieves maximum efficiency as any battery-powered device can achieve longer battery standby time only when the converter is operating at maximum efficiency for the entire load current range, which is particularly important for OLED displays. OLED displays consume the most power when fully white, and for any other display color the current is relatively small, since only white requires all the red, green and blue subpixels to be fully bright. For example, a 2.7 inch display requires 80mA of current to render a full white image, but only 5mA of current is required to display other icons or graphics. Therefore, the OLED power supply needs to reach high converter efficiency for all load currents. To achieve such efficiency, advanced power-saving mode techniques are required to reduce the load current and thus the switching frequency of the converter. Since this is done through a Voltage Controlled Oscillator (VCO), possible EMI problems can be minimized and the lowest switching frequency can be controlled outside the typical 40kHz audio frequency range, which avoids noise generation by the ceramic input or output capacitance. This is particularly important when using such devices in mobile phone applications, and may simplify the design process.

The white light does not consume the maximum power according to the light emitting characteristics, and the power consumption is determined by the brightness value. For example, red, blue, and green, which are 10 luminance values, together produce 30 luminance values of white light. The red, blue and green brightness values are thus adjusted to 3.3 to give a white value (theoretical value) of 10. The same brightness is seen by the human eye from the LED or OLED, and the blue light is consumed most.

Organic light emitting display technology consists of a very thin coating of organic material and a glass substrate. These organic materials emit light when an electric charge passes through them. Since the color of the light emitted from the OLED depends on the material of the organic light-emitting layer, manufacturers can change the material of the light-emitting layer to obtain the desired color. Active matrix organic light emitting displays have built-in electronic circuitry so that each pixel is independently driven by a corresponding circuit. The OLED has the advantages of simple structure, self-luminescence without a backlight source, high contrast, thin thickness, wide viewing angle, high reaction speed, wide use temperature range and the like, can be used for a flexible panel, provides an optimal mode for browsing photos and videos, and has less limitation on the design of a camera.

The increasing complexity and information density of automotive information systems has led to automotive interior displays that are no longer merely basic centralized instrument displays, but rather meet the increasingly detailed and diversified needs of automotive information displays. The market of vehicle-mounted displays is divided into vehicle-mounted navigation devices, vehicle-mounted televisions and vehicle-mounted information systems according to applications; the method is divided into an original market and a later market according to the assembling time. The original market needs to be strictly authenticated, and the original market is difficult to enter; the after-market does not need certification, which is about 20 times of the original market. With the automobile navigation system and the like becoming automobile standard in the future, the proportion of the new automobile equipped with the display, namely the proportion of the original market, will gradually increase.

The display product that automotive electronics needs to require to environmental suitability height, the performance index of the on-vehicle display screen of general demand is: the brightness is 20-60 nit, the normal-temperature working life is 50000 hours, and the tolerance temperature range is-40-85 ℃. In the north american automobile display market, VFDs (vacuum fluorescent displays) have long been popular because they have excellent brightness to ensure good visibility. However, with the advent of OLED, LCD, and liquid crystal display technologies, VFDs are gradually losing their advantages. Because VFDs are power hungry, full color and resolution are greatly limited.

The LCD technology is gradually applied to the field of vehicle display, but the LCD technology is affected by the ambient temperature, which limits the application field of vehicle display products. The liquid crystal material for manufacturing the liquid crystal display screen can become liquid when the environmental temperature is too high, and can become crystal when the temperature is too low, and no matter what kind of state becomes, the liquid crystal material no longer has the photoelectric effect that can receive electric field control, leads to liquid crystal display screen can not normally work, and the contrast, visual angle, the response speed that the liquid crystal shows in addition also change along with the change of temperature, therefore to the on-vehicle demonstration that environmental change is big, liquid crystal is not good display mode.

Compared with the mature TFT-LCD, the OLED (organic electroluminescence display technology) is an active light-emitting display, and has the advantages of high contrast, wide viewing angle (up to 170 degrees), quick response (about 1 mu s), high light-emitting efficiency, low operating voltage (3-10V), ultra-light weight (the thickness is less than 2mm) and the like. The vehicle-mounted display manufactured by the OLED technology has a lighter, thinner and attractive appearance, more excellent color display image quality, wider viewing range and greater design flexibility, and more importantly, the OLED environmental adaptability is far superior to liquid crystal display, and the tolerable temperature range reaches the temperature range of minus 40-85 ℃. And the OLED does not contain lead, and cannot cause environmental pollution. Therefore, the OLED display has great advantages in the field of vehicles.

OLED displays offer great advantages to automotive manufacturers, who can install automotive dashboard lighting systems quickly without the need to punch through wiring on the car as in the past, and OLED technology can give the premium luxury car the perfect feel that represents a significant savings to the luxury car manufacturers and dealers while providing consumer satisfaction. The service life of the OLED is greatly improved, and the service life of 40000-50000 hours in the conventional environment is equivalent to that of a TFT-LCD. The working temperature range of the vehicle-mounted display OLED product reaches-40-85 ℃, the service life of a monochromatic product reaches 55000 hours (70nit) and 50000 hours (80nit), and the working temperature of a vehicle-mounted chip is further improved.

Due to the above advantages, the OLED display screen can be suitably used for POS machines and ATM machines, copying machines, game machines, and the like in the commercial field; the method is applicable to the fields of mobile phones, mobile network terminals and the like in the communication field; the method can be widely applied to PDAs, commercial PCs, household PCs and notebook computers in the field of computers; the product can be used in audio equipment, digital camera, portable DVD; the method is suitable for instruments and meters in the field of industrial application; in the traffic field, the system is used in GPS, airplane instruments and the like.

Flexible screen, refers to flexible OLED. The successful mass production of the flexible screen is not only greatly better than the manufacturing of a new generation of high-end smart phone, but also has a profound influence on the application of wearable equipment due to the characteristics of low power consumption and flexibility, and the flexible screen can be widely applied along with the continuous penetration of a personal intelligent terminal in the future.

The flexible screen mobile phone is a mobile phone with a flexible and good-flexibility screen, and is also called as a awn mobile phone because of being shaped like a awn roll.

OLEDs are thin and can be mounted on flexible materials such as plastic or metal foils. Instead of glass, plastic can make the display more durable and lighter. The flexible OLED panel is concave from top to bottom with a bending radius of 700 mm.

The OLED adopts a plastic substrate instead of a common glass substrate, and a protective film is adhered to the back surface of the panel by means of a thin film packaging technology, so that the panel can be bent and is not easy to break. The flexible screen can be rolled but cannot be folded, future products can be folded, and the appearance can be changed more.

The display screen is cut from the panel. Flexible displays, also known as flexible screens, are seen as a preliminary product of the display screen revolution, with the ultimate goal of turning mobile and wearable electronics around.

The OLED preparation scheme is that the organic functional layer and the cathode layer are prepared by adopting a vacuum evaporation technology, so that expensive evaporation equipment is needed, the production cost is high, and the production efficiency is low. Meanwhile, the preparation of a large-area display screen is difficult to realize due to the size of vacuum evaporation equipment. Compared with vacuum thermal evaporation, the solution method has the advantages of simple operation, low cost and the like, and is suitable for preparing large-size OLED screens at low temperature or room temperature. With the rapid iteration of organic electronic technology, liquid phase processing technology of soluble organic materials is becoming mature, and the preparation of OLEDs by liquid phase methods, especially by printing processes, is considered to be one of the key methods for solving the development bottlenecks of the existing OLEDs.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

The pixel driving circuit and the display panel provided in the embodiments of the present application are described in detail above, and a specific example is applied in the description to explain the principle and the implementation of the present application, and the description of the embodiments above is only used to help understanding the technical solution and the core idea of the present application; those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure as defined by the appended claims.

Claims

1. A pixel driving circuit, comprising:

a write transistor having a first gate, a second gate, the first gate connected to the second gate; and

a drive transistor having a third gate, a fourth gate, one of the source/drain of the write transistor being connected to the third gate and the fourth gate.

2. The pixel driving circuit according to claim 1, further comprising:

and one end of the storage unit is connected with the third grid electrode, and the other end of the storage unit is connected with one of the source electrode and the drain electrode of the driving transistor.

3. The pixel driving circuit according to claim 2, further comprising:

and a first end of the light emitting unit is connected with one of the source electrode and the drain electrode of the driving transistor, and a second end of the light emitting unit is used for accessing a first power supply signal.

4. The pixel driving circuit according to claim 3, wherein the other of the source/drain of the driving transistor is configured to receive a second power signal.

5. The pixel driving circuit according to claim 4, wherein a potential of the first power supply signal is lower than a potential of the second power supply signal.

6. The pixel driving circuit according to claim 3, wherein the storage unit comprises:

and one end of the storage capacitor is connected with the third gate, and the other end of the storage capacitor is connected with one of the source/drain of the driving transistor.

7. The pixel driving circuit according to claim 6, wherein the light emitting unit comprises:

a light emitting device having an anode connected to one of the source/drain of the driving transistor and a cathode connected to the first power signal.

8. The pixel driving circuit according to any one of claims 1 to 7, wherein the channel type of the writing transistor is different from that of the driving transistor; and the writing transistor is a P-channel type thin film transistor.

9. The pixel driving circuit according to any one of claims 1 to 7, wherein the channel material of the writing transistor and the driving transistor is the same; and the channel material of the driving transistor comprises at least one of indium, gallium and zinc.

10. A display panel comprising the pixel drive circuit according to any one of claims 1 to 9.