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DLP9000: DLP9000 surface curvature

Alan Bell
Prodigy 60 points
Part Number: DLP9000
Other Parts Discussed in Thread: DLP7000

Hi all,

We are investigating the use of DMDs (specifically the DLP9000) in an optical correlator. For this application, the device needs to have very little curvature and not be under and intrinsic stress which could cause aberrations or birefringence.

During our investigations, we made some interferometry measurements of the mirror arrays in the powered up and powered down states.  The image below shows the results when the evaluation board is powered down so that the mirrors are set flat and parallel to the glass surface. There is significant curvature. 

Has anyone else made similar measurements? Is this normal for this device?

Can Texas Instruments do anything in their production to prevent the curvature? We suspect it could be due to shrinkage of the epoxy at the corners of the DMD device that holds it to its ceramic base plate. This shrinkage may be inducing small stresses on to the device, making it unusable for our application.

I'd be interested to hear from anyone who has made similar measurements or found a solution to reduce this curvature.

Regards.

A.

  • 0
    TI__Mastermind 49105 points

    Hello Alan,

    Welcome to the DLP section of the TI-E2E forums.

    There are two specs that may be of interest you you:

    • Most of the DMD data sheets should have a "Window Characteristics" section that specifies the Window Flatness in fringes/25 mm of 632.8 nm light.
    • In the mechanical ICD attached to the end of the data sheet there should be information on "Die Parallelism tolerance" and "Die Height tolerance" and where the measurement applies. 

    These are the only specifications that we provide on this.

    Fizix

  • 0 in reply to Fizix
    Prodigy 60 points

    Thank you Fizix.

    I don't see either of those characteristics in the specifications for the DLP9000.  We are considering purchasing the DLP6500 as an alternative, but again, I don't see any specification of curvature or window flatness in the relevant datasheet.

    If our suspicions are correct, the curvature is caused by the final assembly of the DMD device to its ceramic PCB, with the epoxy contracting as it cures, therefore putting stresses on to the otherwise flat DMD structure.

    Are TI open to the idea of trying a different epoxy for bonding the DMD? One that doesn't contract and induce stress?

    Can you provide any information relating to flatness of the glass and mirrors for the DLP9000 and/or the DLP6500 ?

    Thanks,


    A.

  • 0 in reply to Alan Bell
    TI__Mastermind 49105 points

    Hello Alan,

    You are correct that the DLP9000 data sheet does not seem to include the Window Flatness numbers.  The numbers from the DLP7000 are fairly typical.  Not sure why it is not included.

    Regarding the second bullet, the referenced items can be found as callouts in square boxes 10 & 11 (12 is also related) on page one of the ICD:

    Fizix

  • 0 in reply to Fizix
    Prodigy 60 points

    Thanks Fizix,

    It looks like we're seeing slightly more curvature in the device than the datasheet tolerances would allow. We'll have to see if we can correct for this somehow. Thanks for your assistance.

  • 0
    Prodigy 190 points
    Dear Alan Bell,
    Could you tell me where you bought dlp9000 (TI, Vialux, keynotephotonics , etc)?And did you find the kHz-frequency switching noise? To avoid mirror getting stuck , some manufacture implement a switching cycle which applies the MCP(mirror clocking pulse) every clock cycle, even if the pattern has not been updated,which kHz-frequency switching noise. You can find the detailed information from the article ‘suppression kHz-frequency switching noise in the digital micro-mirror devices’.
    Best Regards,
  • 0 in reply to Peter678
    Prodigy 60 points

    Hello Peter,

    We purchased the DLP9000 from DigiKey (USA) as part of the Evaluation Module. We haven't noticed any high-frequency switching noise. We're running at a slow frame rate (30Hz) with the camera. I see your forum communication with TI regarding this issue, and they state that they don't implement a switching cycle on static images on the EVM module (Although it is advised to implement such a cycle in a final product design to prolong the DLP lifespan).

    So, if you plan to use the DLP9000 EVM for your R&D, I don't think you need to be concerned about high frequency switching noise on static images. But you may want to limit the time that it displays static images, and run some non-static images through the device when it's not in use to prevent mechanical memory in the micro hinges.

    Best regards,

    Alan.

  • 0 in reply to Alan Bell
    Prodigy 190 points
    Thank you very much Alan.