Measuring the Output Performance of UV LEDs

Transcription

1 Measuring the Output Performance of UV LEDs Paul Mills May 2012

2 UV LED Measurement: We have the answers, but what are the questions?

3 MEASURING LocaCon, THE OUTPUT On The PERFORMANCE Free OF UV LEDS Home on LocaCon, Same Samples the Range LocaCon Wavelength Under the Lens It s a Numbers Game

4 Trends in UV LEDs 1. Higher Output 2. More Wavelength Choices 3. Broader Spectrum Coverage 4. More Pulsed Control Schemes 5. Increasing use of OpCcs

5 In 2002 commercial UV LEDs Produced about 100mW/cm 2

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7 UV LED Output Growth In 10 years UV LED Output has increased 100-fold from 100 mw/cm 2 to over 10W/cm 2

8 UV LED Output Growth In 10 years UV LED Output has increased 100-fold from 100 mw/cm 2 to over 10W/cm 2 Which is a common occurrence for semi-conductor technology in general

9 UV W/cm 2 40 mw

10 Radiometers must have sufficient dynamic range to accurately measure high-intensity sources without attenuating the measured signal.

11 Q: What is the expected irradiance of UV LEDs?

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16 UV OpCcal Window/Filter Diffuser(s) 0.50 Aperture opening(s) OpCcal Filter Silicon Photodiode or other type detector

17 Filter- Detector- Composite Responses op6cal stacks must be tested Filter Detector Composite

18 There has been continued improvement in Designing radiometers that are optimized for the wavelengths being supplied by the market.

19 Q: What wavelengths do we need to measure for UV LEDs?

20 Heat limits how hard LEDs can be driven. Pulsing the diode allows it to be driven to higher output levels by not energizing the die for 100% of the time.

21 Irradiance mw/cm 2 To compute energy density a series of sample irradiance measurements are added together

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23 Some UV light sources, like pulsed Xenon lamps require extremely fast sampling to accurately capture the lamps emission.

24 Time Microseconds

25 Smoothing On = 6,795 mw/cm 2 Smoothing Off = 10,459 mw/cm 2 Energy Density = 2,568 mj/cm 2 Fast sampling can capture variations In lamp intensity with power supply changes.

26 Pulsing the LED light source directly affects actual energy density compared to the instruments calculat

27 Q: What is the control scheme for LEDs and should measurement instruments compensate for them?

28 The measurement device is intended to simulate the part surface in a production environment.

29 E θ = E x Cosθ θ Cosine Error in Measurement

30 45 o =.7 Watt 90 o = 1.0 Watt θ Cosine Error in Measurement

31 We have learned to design Instruments that accurately simulate conventional light sources

32 But LED arrays are being supplied in a wider range of configurations

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35 Optical diffusers and lenses on dies and arrays could significantly affect the radiant footprint of the light source and change the proper spatial response.

36 Spatial Response of Instruments Goal: Cosine Response

37 Q: What it the proper cosine response for LED arrays?

38 Irradiance falls off quickly as we move away from the source in any direction.

39 Table Courtesy of Phoseon Technology

40 Courtesy of Integration Technology

41 Q: Where should UV LED measurements be made?

42 1. Better dynamic Range 2. Fast sampling & Smoothing 3. All wavelengths 4. Perfect cosine response The right instrument needs to address a wide range of desirable features. 5. Inexpensive as Possible!

43 Q: How much should a radiometer cost?

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45 Quantitative, routine maintenance Real-time status monitoring

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47 MEASURING THE OUTPUT PERFORMANCE OF UV LEDS A sensor in the process chamber detects changes in UV irradiance

48 MEASURING STATIC VERSUS THE REAL- TIME OUTPUT PERFORMANCE MEASUREMENT OF UV LEDS Two kinds of UV measurement Absolute Measurement Want a number Match a specificacon Troubleshoot OpCmize a process Compare mulcple lines Communicate data RelaCve Measurement Want to compare UV changes with Cme Alarms Constant monitoring Simultaneous readings

49 MEASURING ONLINE MONITORING THE OUTPUT & PERFORMANCE MEASUREMENT OF UV LEDS Off-the-Shelf Standard Interface Solutions

50 Q: What is the purpose of your measurement? What is the number used for?

51 Decision Makers

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55 Lamp Designers Formulators End Users Machine Designers Instrument Designers

56 Q: Who will lead the discussion that will shape how LEDs are measured?

57 Paul Mills Penny Jim Raymont

58 Thank You! Paul Mills EIT LLC