LCD上集成金屬膜型熱傳感器溫度補償系統-韓國留學生dissertation Integrated Thermal Sensor on LCD for Temperature

Compensation System

Ki-Chan Lee, Yun-Jae Park, Haeng-Won Park, Taesung Kim,

Seung-Hwan Moon, Brian H. Berkeley and Sang-Soo Kim

Advanced Product Development Team, LCD Development Center, LCD Business,

Samsung Electronics, Asan-si, Chungnam-do, Korea

摘要 Abstract

This paper presents a thermal sensor which has been integrated onto an LCD. 該傳感器采用金屬（鉬/鋁）薄膜作為溫度檢測層，以及其制造不需要制造流程的變更。The sensor uses metal (Mo/Al) film as a temperature detection layer, and its fabrication requires no manufacturing process changes.    http://ukthesis.org/Thesis_Writing/Accounting_Assignment/Engineering/ 傳感器顯示了很好的線性度，靈敏度

和可靠性。The sensor shows very good linearity, sensitivity and reliability. Used with a feedback system, the thermal sensor resulted in flicker reduction of nearly 70% over the temperature range 10℃ to 70℃.vv

簡介 1. Introduction

面板上的TFT液晶顯示器的光學特性明顯取決于溫度。Optical characteristics of TFT LCDs depend significantly on panel temperature [1]-[3]. For instance, the rotational viscosity of liquid crystals decreases at low temperature, leading to slow response time and motion blurring. Ambient conditions and the internal backlight cause the LCD panel temperature to change. LCD panel temperature changes can lead to unbalanced pixel driving voltage,which can result in flicker noise when using inversion driving. To compensate for the various temperature dependencies, a thermal sensor with feedback control could serve as a useful solution.

However, it is complicated to accurately detect temperature of the LCD panel, because a conventional sensor can not be placed at the center of the panel without directly blocking pixels. Furthermore,because the LCD panel is placed between the ambient air and heat generating components within the TV or monitor set, there is a high temperature gradient from the front to the back of the panel.

Also, temperature differences between the upper and lower portions of the panels surface can exceed 10 in large sized (>32”) TFT LCDs. Therefore, to accurately detect temperature in large size panels, at least two sensors are needed, one each for the upper and lower portions of the display. Additionally, measurement accuracy and response time are affected by the thermal resistance of the sensor as attached to its mounting pad.

For a discrete thermal sensor, the best place for attachment would either be at the corner or along the edge of the panel frame. However, considering backlight and ambient heat source dependencies, the best place to measure the panel temperature is on the LCD panel itself. Furthermore, the best internal placement point is at the same layer as the actual liquid crystal. Practically, it is impossible to make a thin and small thermal sensor to be installed within the liquid crystal layer. It is also difficult to attach#p#分頁標題#e#

an external sensor and its circuitry to the LCD glass along the narrow black border around the edge of the panel. Moreover, doing so would increase production cost and process time.

In our work, 我們已經開發了一種新的準確測量溫度的技術。我們的方法是使用一個金屬門電阻傳感器集成到LCD面板中。we have developed a new technology for measuring the temperature accurately. Our approach uses a gate metal resistor sensor integrated onto the LCD panel, as depicted in

 

金屬薄膜型熱傳感器 2. Metal film-type thermal sensors

Many kinds of thermal sensors, including thermistors and thermocouples, have already been commercialized, and these have rapid response time and low cost [4]. However, these sensors have an inherently severe nonlinearity so as to require signal processing apparatus for accurate measurement. Furthermore, these sensors show low reliability in long term tests. By comparison, metal filmtype thermo-resistors show good linearity and long term reliability, but are more expensive. Efforts are underway to apply

recently-developed IC-type thermal sensors to overcome these inherent problems and enhance functionality by including signal conditioning and interface blocks within the CMOS technology.

At the same time, to achieve accurate temperature measurements on a relatively large and thin medium, several sensors and good placement will inevitably be required. Unfortunately, there are significant obstacles toward attaching multiple thermal sensors to the liquid crystal layer sandwiched within the glass without

creating opacities.

In this paper, 我們采取一種新的方法，整合熱傳感器到液晶面板使用金屬柵（鉬/鋁）探片。we take a new approach, which is to integrate the thermal sensor onto the LCD panel using gate metal (Mo/Al) as the detective film. A photograph of the new sensor is shown in Figure 2.

Driver IC FPC Border of BM Thermal sensor

熱傳感器的工作使用的固有特性金屬，其結果表現出溫度隨著電阻的變化而變化。The thermal sensor operates by using the inherent properties of metals, which exhibit a change in electrical resistance as a result of a change in temperature. The sensor has a positive temperature coefficient. Its resistance (RS) is directly proportional to the metal film’s length (L), and inversely proportional to the crosssectional area (WD), per equation (1). Normally, the resistivity is described accurately by a second order polynomial. The resistivity (ρ) of detective metal film (Mo/Al) in equation (2) is approximately linear in the temperature range, -10℃ to 80℃.

Resistivity (ρ ) of the sensor depends on temperature (T) and reference resistivity (ρ 0) at a standard temperature of 0℃. All metals have a specific and unique resistivity that can be determined experimentally.#p#分頁標題#e#

The fabricated metal film resistor can be connected to an external resistor (Rc) to form a simple resistive divider circuit as shown in

Figure 3. This circuit provides the readout voltage (Vout) from the driving voltage (VS) in equation (3).

3.金屬膜熱傳感器的自熱  Self-heating in the metal film thermal sensor

要測量電阻，有必過使電流流過金屬電阻。加熱電阻兩端產生的電壓降的移動設備稱為焦耳加熱的效果，它依賴于電流密度。To measure resistance, it is necessary to pass a current through the metal resistor. The resultant voltage drop across the resistor heats the device in an effect known as Joule heating, which depends on current density. Therefore, the sensor indicates a temperature that is slightly higher than the actual temperature. The amount of selfheating

also depends heavily on the medium in which the sensor is immersed. Our fabricated sensor is sandwiched between the top and bottom LCD glass. In this position, the self-heating effect is much less compared to open-air placement due to heat sinking of the sensor by the liquid crystal material and glass substrate.
To decrease self heating, resistance (>1 kΩ) of the metal sensor was designed to be relatively higher than that of conventional commercial sensors.

4. 傳感器的性能 Fabricated sensor performance

To test sensor performance and reliability, four thermal sensor samples were produced using our standard production line. The sensor’s output voltage has good repeatability and linearity over the range of operating temperatures as shown in Figure 4. The difference of each sensor output results from the variation of film

thickness and width in the fabrication process. The external resistor needs a low temperature coefficient for improved system performance. The sensor output spans about 0.4V over the temperature range of -10℃~ 80℃.

(1)

ρ ≈ ρ +α 0 (1 T) (2)

R L

S WD = ρ

V = (3) R

R +R

V out

C

S C

S

Figure 2. Photograph of fabricated thermal sensor on LCD

SiN/Mo/Al/Glass

7μm

Metal film width

VS

IS

RC

Vout

Heat RS

 

-10 0 10 20 30 40 50 60 70 80

Temperature (℃)

Voltage (V)

23P-1-H1-D00

23P-2-H1-D00

23P-3-H1-D00

23P-4-H1-D00

Figure 4. Experimental results of sensor output voltage versus

temperature, Vs=5V, Rc=1.6kΩ

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 #p#分頁標題#e#

The fabricated sensor’s reliability was measured by applying 15 temperature cycles as shown in Figure 5. There was little deviation of the sensor’s output voltage during the 270 hour experiment. Recently, stability testing has passed 500 hours. Gate metal film stability of TFT-LCDs has already been proven in mass production and commercialization. The fabricated sensor characteristics show good linearity, repeatability, and stability as

summarized in Table 1.

5. Temperature compensation on flicker

Most electronic components, including TFT LCD panels, are inherently affected by temperature. The a-Si TFT channel mobility and off-state hole current significantly depend on temperature.

Additionally, permittivity of liquid crystal material is also temperature dependent. Column and row drive ICs in the TFT LCD can be affected by applied thermal energy. These thermal influences can lead to unbalanced pixel driving voltage, resulting in flicker when using inversion driving in the LCD panel.
To balance the positive and negative pixel voltages (Vp) and thereby minimize flicker noise, the common voltage (Vcom) in Figure 6 should be tuned to compensate temperature changes. The experimentally proven results suggest that the common voltage should be proportional to the temperature variation in order to minimize flicker.

Parameter Value

Sensitivity 0.377 [%Ω/℃]

Repeatability 98 [%FS]

Selectivity No reaction to light

Stability 98 [%FS] @500hr

Linearity 96 [%FS]

Test range -10 ~ 80 ℃

Size 4 mm x 2 mm

Figure 5. Sensor consistency over multiple cyclic temperatures

2.10

2.20

2.30

2.40

2.50

2.60

2.70

2.80

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

Time (min)

Voltage (V)

23P-1-H1-D00 23P-2-H1-D00

23P-3-H1-D00 23P-4-H1-D00

Table 1. Spec summary of integrated thermal sensor

 

Heat

Figure 6. Thermal impact on pixel voltage balance

Figure 7. Block diagram of temperature compensation

system

LCD Panel

Thermal sensor

-

+

R2

R3

RS

R1

AVDD

F-VCOM VCOM

Calibration PC

IIC

Flicker tuning

Thermal

sensor

Temp

Rs

Digital variable

resistor (DVR)

Rset

LCD Panel

Thermal sensor

Temp. Chamber

Optical probe#p#分頁標題#e#

Operator

DVR tuner

Flicker meter

Test pattern

Figure 8. Experimental setup to evaluate thermal sensor

system performance

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A block diagram of the Vcom compensation system based on the integrated thermal sensor is shown in Figure 7. The system includes a means to program Vcom digitally with a digital variable resistor (DVR). The characterized sensor and systems compensate the common voltage when the temperature changes.

Figure 8 shows the experimental setup for evaluation of the temperature compensation system. Flicker was minimized by tuning the common voltage with a programmable setting at the initial room temperature. Then, flicker was measured as the chamber temperature changed from 10℃ to 70℃. Figure 9 shows flicker levels with and without the feedback compensation system. Over the range of temperatures tested, the thermal feedback compensation system reduced flicker by approximately 70% compared to the uncompensated panel.

6. Impact

我們已經制作了金屬膜（鉬/鋁）型熱感應器在LCD上。它具有良好的精度，線性度，靈敏度和不需要增加制造時間或成本。We have fabricated a metal film (Mo/Al) type thermal sensor onto an LCD. It has good accuracy, linearity, sensitivity and reliability and does not required increased fabrication time or cost. This integrated thermal sensor can significantly reduce thermallyinduced flicker using a simple, low cost analog feedback system.

Additionally, LCD panel response time characteristics are significantly dependent on the LC material temperature. The integrated sensor will be used as a key component to provide a low cost means to compensate LCD overdrive values in order to offer temperature-invariant performance. This sensor and feedback technique can also be applied to other display types such as OLEDs and PDPs, which also have inherent temperaturedependent characteristics.

7. References

[1] Mitsuhiro Shigeta, Hirofumi Fukuoka, “Recent Development

of High Quality LCD TV”, SID’04 Digest, pp. 754-757, 2004.

[2] S. Naemura, H. Ichinose, A. Sawada, “Liquid-Crystalline

Materials for TFT-Addressed Displays with Improved Image-

Sticking Properties”, SID’97 Digest, pp. 199-202, 1997.

[3] H. J. Park, Luc. Lai, S.H. Lin, K.H. Yang, “Analysis of IPS

Mura, Image-Sticking and Flicker Caused by Internal DC

Effects”, SID’03 Digest, pp. 204-207, 2003.

[4] Julian W. Gardner, Microsensors, John Wiley & Sons Ltd, pp.

93-107, 1994.