Performance of Chemical Vapor Deposited Boron-Doped AlN Thin Film as Thermal Interface Materials for 3-W LED: Thermal and Optical Analysis

doi:10.1007/s40195-017-0592-5

Abstract

Abstract:

Boron-doped aluminum nitride (B-AlN) thin films were synthesized on Al substrates by using chemical vapor deposition method by changing the synthesis parameters and were used as thermal interface material for high power light emitting diode (LED). The B-AlN thin film-coated Al substrate was used as heat sink and studied the performance of high power LED at various driving currents. The recorded transient cooling curve was evaluated to study the rise in junction temperature (T _j), total thermal resistance (R _th-tot) and the substrate thermal resistance (R _th-sub) of the given LED. From the results, the B-AlN thin film (prepared at process 4) interfaced LED showed low R _th-tot and T _jvalue for all driving currents and observed high difference in R _th-tot (ΔR _th-tot = 2.2 K/W) at 700 mA when compared with the R _th-tot of LED attached on bare Al substrates (LED/Al). The T _j of LED was reduced considerably and observed 4.7 °C as ΔT _j for the film prepared using process 4 condition when compared with LED/Al boundary condition at 700 mA. The optical performance of LED was also tested for all boundary conditions and showed improved lux values for the given LED at 700 mA where B-AlN thin film was synthesized using optimized flow of Al, B and N sources with minimized B and N content. The other optical parameters such as color correlated temperature and color rendering index were also measured and observed low difference for all boundary conditions. The observed results are suggested to use B-AlN thin film as efficient solid thin film thermal interface materials in high power LED.

Key words: Light emitting diode (LED), B-AlN thin film, Chemical vapor deposition (CVD), Thermal transient analysis, Junction temperature, Optical performance

S. Shanmugan, D. Mutharasu. Performance of Chemical Vapor Deposited Boron-Doped AlN Thin Film as Thermal Interface Materials for 3-W LED: Thermal and Optical Analysis[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(1): 97-104.

Figures/Tables 9

Table 1 Deposition parameters of B-AlN thin film coating by CVD

Process	Source material	Carrier gas (N₂) flow rate (sccm)	Average film thickness (nm)
Process 1	AlCl₃	10	423
	tert-buthylamine	25
	BCl₃	25
Process 2	AlCl₃	2.5	498
	tert-buthylamine	15
	BCl₃	15
Process 3	AlCl₃	5	440
	tert-buthylamine	25
	BCl₃	25
Process 4	AlCl₃	5	418
	tert-buthylamine	10
	BCl₃	10

Fig. 1 Schematic diagram of synthesis of B-AlN thin film using CVD method

Fig. 2 Schematic diagram of LED mounted on B-AlN-coated Al Substrate $ \Delta T_{\text{j}} = \, \Delta V_{\text{F}} K. $ (1)

Fig. 3 Cumulative structure function of 3-W green LED fixed on B-AlN-coated Al substrates measured at 700 mA

Fig. 4 Zoomed version of cumulative structure function curve of 3-W green LED fixed on B-AlN-coated Al substrates measured at a100 mA, b 350 mA, c 700 mA

Table 2 Thermal resistance of 3-W green LED fixed on substrate prepared at various process conditions

Driving currents (mA)	Bare Al	Process 1	Process 2	Process 3	Process 4
Junction to ambient total thermal resistance, R _th-tot (K/W)
100	46.96	47.40	46.70	46.43	45.67
350	44.18	45.43	44.78	44.71	43.52
700	45.74	45.94	44.85	44.98	43.54
Board to ambient (substrate) thermal resistance, R _th-tot (K/W)
100	34.64	34.13	33.09	33.63	33.02
350	31.70	32.64	31.31	31.53	30.34
700	29.81	29.50	28.89	29.08	27.68

Fig. 5 Variation of measured T j of 3-W LED fixed on bare and B-AlN thin film-coated Al substrates prepared at various process parameters

Fig. 6 Change in R th-sub of bare and B-AlN thin film-coated Al substrates for process parameters at various driving currents

Fig. 7 Influence of B-AlN coatings on lux of 3-W green LED at a 100 mA, b 350 mA, c 700 mA

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