内置传感器LED的热阻与TIM评估新方法

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本文档深入探讨了"使用内置传感器的LED进行LED热阻和TIM评估的研究"这一主题。作者团队由Xiaoli Wang、Yugang Zhou、Renbao Tian等人组成，他们在2017年的IEEE Photonic Technology Letters第29卷第21期发表的研究中，针对传统方法存在的测量延迟问题，提出了一种创新的方法来精确评估LED的热阻和热界面材料（TIM）。这种方法结合了稳态和瞬态热测量技术，显著减少了由于电流切换导致的测量延迟，提高了测量的准确性。在传统的LED热阻和TIM评估中，由于电流的开关过程，可能会引入测量误差，特别是在确定结温（junction temperature）时，由于自发光效应可能导致轻微偏差。然而，通过使用内置传感器的LED，研究者能够消除这种延迟问题，并在稳态测量中识别并补偿因自发光引起的温度测量误差，使其在实际应用中影响微乎其微。此外，与传统方法相比，这种方法利用成本较低的设备实现了更高的精度。文章的关键术语包括结温、热阻、发光二极管（Light Emitting Diodes, LEDs）以及热界面材料。这项研究不仅对提高LED器件的性能和可靠性具有重要意义，也为相关领域的研究者提供了新的测量策略和技术参考。通过改进的LED内置传感器技术，研究人员得以更有效地监控和控制LED的工作温度，从而优化其工作效率和寿命，对于LED照明、显示屏等领域的设计优化具有深远影响。

1856 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 29, NO. 21, NOVEMBER 1, 2017

Study of LED Thermal Resistance and TIM

Evaluation Using LEDs With Built-in Sensor

Xiaoli Wang, Yugang Zhou, Renbao Tian, Bin Liu, Zili Xie, Rong Zhang, and Youdou Zheng

Abstract—This study developed an LED thermal resistance

and thermal interface material evaluation method using LEDs

with an internal sensor unit by both steady-state and transient

thermal measurements. The problem of the measurement delay

time caused by the current switching, which exist in conventional

methods can be avoided in both steady-state and transient

thermal measurements. Slight error in junction temperature mea-

surement caused by the self-illumination effect can be identiﬁed

without the current switching issue. The error is compensated in

steady-state thermal measurement and is insigniﬁcant in transient

measurement. Compared with conventional methods, this method

uses low-cost equipment, while realizing improved accuracy.

Index Terms— Junction temperature, thermal resistance, light

emitting diode, thermal interface materials.

I. INTRODUCTION

IGHT emitting diodes (LEDs) have become a new

generation of solid-state lighting sources due to their

advantages of long lifetime, low power consumption, short

response time, and environmental friendliness [1]. Junction

temperature and thermal resistance are critical to character-

ize the thermal performance of LED products [2]. Thermal

interface materials (TIM) are one of the most critical factors

for thermal performance and reliability of the LED package.

A fast and accurate junction temperature (T

) measurement

method contributes to the judgement of TIM performance.

The forward voltage method is commonly applied for T

measurements [3]–[5]. Using the conventional forward voltage

method, the forward current will switch between working

current and small measurement current. Measurement delay

time (t

) must be considered for two reasons: either the test

system cannot switch fast enough to ensure accurate voltage

measurement, or the device cannot switch fast enough due

to excessive capacitance or other circuit problems [5]. With

non-zero t

, the junction cooling or heating after switching

will cause measurement errors. This means that expensive and

complicated equipment is required to enable fast switching

Manuscript received June 29, 2017; revised August 26, 2017; accepted

September 11, 2017. Date of publication September 18, 2017; date of current

version October 13, 2017. This work was supported in part by the National

Natural Science Foundation of China under Grant 61334009 and Grant

61634005, in part by the National Key Research and Development Program of

China under Grant 2016YFB0400904, in part by the Collaborative Innovation

Center of Solid-State Lighting and Energy-Saving Electronics and in part by

the Project Funded by the Priority Academic Program Development of Jiangsu

Higher Education Institutions. (Corresponding author: Yugang Zhou.)

The authors are with the Jiangsu Provincial Key Laboratory of Advanced

Photonic and Electronic Materials, School of Electronic Science and Engineer-

ing, Nanjing University, Nanjing 210023, China (e-mail: ygzhou@nju.edu.cn).

Color versions of one or more of the ﬁgures in this letter are available

online at http://ieeexplore.ieee.org.

Digital Object Identiﬁer 10.1109/LPT.2017.2753942

Fig. 1. (a). bare-chip photograph of LED chip with internal sensor;

(b) the photograph of the LED package mounted on MCPCB.

Fig. 2. The structure of LED samples with TIM.

and smaller t

for precise measurement of transient T

and

further analysis of structure function of LED and evaluation

of TIM.

In a previous study, we proposed a novel LED structure with

an internal sensor unit for T

measurement without current

switching [6]. For this letter, we further studied the evaluation

of thermal interface material and LED thermal properties using

this novel LED structure. Both the junction-to-ambient steady

thermal resistance and transient thermal impedance of LEDs

with different TIM were studied.

II. E

XPERIMENTAL DETAILS

Blue LED chips with an internal sensor unit were used

in this study, and the chip structure has previously been

described [6]. Isolated LED unit and sensor unit were inte-

grated into a single chip, as is shown in Fig. 1(a). The whole

chip size is 750 × 500 μm

. The effective light-emission

area of the LED unit is around 750 × 430 μm

and the

effective p-n junction area of the sensor unit is around

96 × 96 μm

. The chips were packaged using a four-lead

high-power leadframe, then the packages were mounted on

a metal-core printed circuit board (MCPCB), as is shown in

Fig. 1(b). Fig. 2 shows the thermal dissipation structure of

LED samples shown in Fig.1(b). The forward voltage of the

sensor diode was used to characterize the junction temperature

after calibration.

Three parts of the experiments were performed. The ﬁrst

measured the transient T

, using the internal sensor and

See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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