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Mattrix CEO Answers Our Questions on Its LTPS/IGZO Replacement
Max Lemaitre, Ph.D., CEO & Founder of Mattrix was kind enough to respond to the questions we raised last week regarding Ian Hendy’s Display Daily’s article on VOLET technology as a lower cost substitute for LTPS or IGZO.
Max Lemaitre, Ph.D., CEO & Founder of Mattrix was kind enough to respond to the questions we raised last week regarding Ian Hendy’s Display Daily’s article on VOLET technology as a lower cost substitute for LTPS or IGZO.
Mattrix’s OLET combines current control with light emission by integrating the drive transistor, storage capacitor and light-emitting stack into one device. Mattrix claims by eliminating the compensation circuitry it reduces the # of TFTs and Cs blocking the light in a top-emission active matrix OLED.
OLED-A: The article provided no specs on the reliably and mobility of the TFTs, a very strange way to discuss the subject.
Max Lemaitre: Your point is well taken. The article was intended to introduce Mattrix and our new prototype, and as such was intended for a non-technical audience.
Since a-Si mobility is ~0.7 cm2.v*sec and LTPS is ~100 and IGZO ~20, a-Si TFTs needs to be 20 to 100 times larger, which would be a limiting factor on resolution.
Mattrix only uses a-Si for the switching-TFT.
Max Lemaitre: Since it is only acting as a voltage switch it does need not be large relative to the pixel area. In a conventional pixel, you would be absolutely correct, however the key innovation here is Mattrix’s vertical light emitting transistor (VOLET), which combines the drive-TFT, storage cap, and OLED into a single, highly stable, vertically stacked device. This eliminates the need for a separate drive TFT and in-pixel compensation circuitry. The result is a very simple, two-component pixel: 1 a-Si sw-TFT and 1 VOLET.
OLED-A: The larger TFTs, would reduce the aperture ratio does not increase it.
The reduction in aperture comes from the elimination of a separate drive-TFT, storage cap, and compensation TFTs.
Max Lemaitre: Of course we could increase the aperture ratio further by using an IGZO switching-TFT, but that is not necessary in the case of TV applications (using our technology).
OLED-A: It is unlikely that any panel maker would go the route of WRGB design for a smartphone due to the need for precise control, very high max luminance and absorbing 50% color filter losses.
Max Lemaitre: Agreed. This prototype specifically demonstrates how our technology would be implemented in a TV application. We have another prototype which we are working on with Samsung Advanced Institute of Technology which demonstrates the mobile use case (more on this below).
OLED-A: a-Si TFTs tend to suffer from wide variations in the gate voltage, which is a major problem for OLED’ drive TFTs, where the turn-on and turn-off voltages must be precisely controlled.
We do not use a-Si for the drive TFT for these very reasons. Our VOLET device - which can be thought of as a gated-OLED or light emitting triode - is very stable (i.e. negligible Vth shift after 9 months of continuous operation) and allows us to avoid using a-Si for the drive TFT entirely.
OLED-A: The claim that backplanes contribute 20% of the yield loss is absurd, as it tends to be in the 1% range out of the total yield loss of ~20%.
Max Lemaitre: I can’t comment on this with much authority, however in our discussions with panel makers, OLED backplane yields still appear to be a significant issue, especially for IGZO.
OLED-A: The technique would be less expensive and use less masks than LTPS or IGZO but converting an LCD fab to OLEDs needs 3/4 of the OLED capex for the deposition and encapsulation process and more space for a comparable capacity.
Max Lemaitre: Agreed. Our claim is simply that we reduce the total Capex costs as a result of the conversion, and additionally reduce opex cost by simplifying the manufacturing process.
OLED-A: Then there is the matter of LTPO and VRR, given that the cumulative number of OLED panels with LTPO for Samsung and Apple will be 350m+ going forward. And it is likely that new tablets and notebooks will also use LTPO."
Max Lemaitre: Glad you point this out - we completely agree. That is why our other prototype (with Samsung) is based on an IGZO switching-TFT combined with our VOLET. This combination actually allows for even lower frequency operation (<0.2Hz) and requires less than 30% of the mask steps of LTPO.
OLED-A: The article provided no specs on the reliably and mobility of the TFTs, a very strange way to discuss the subject.
Max Lemaitre: Your point is well taken. The article was intended to introduce Mattrix and our new prototype, and as such was intended for a non-technical audience.
Since a-Si mobility is ~0.7 cm2.v*sec and LTPS is ~100 and IGZO ~20, a-Si TFTs needs to be 20 to 100 times larger, which would be a limiting factor on resolution.
Mattrix only uses a-Si for the switching-TFT.
Max Lemaitre: Since it is only acting as a voltage switch it does need not be large relative to the pixel area. In a conventional pixel, you would be absolutely correct, however the key innovation here is Mattrix’s vertical light emitting transistor (VOLET), which combines the drive-TFT, storage cap, and OLED into a single, highly stable, vertically stacked device. This eliminates the need for a separate drive TFT and in-pixel compensation circuitry. The result is a very simple, two-component pixel: 1 a-Si sw-TFT and 1 VOLET.
OLED-A: The larger TFTs, would reduce the aperture ratio does not increase it.
The reduction in aperture comes from the elimination of a separate drive-TFT, storage cap, and compensation TFTs.
Max Lemaitre: Of course we could increase the aperture ratio further by using an IGZO switching-TFT, but that is not necessary in the case of TV applications (using our technology).
OLED-A: It is unlikely that any panel maker would go the route of WRGB design for a smartphone due to the need for precise control, very high max luminance and absorbing 50% color filter losses.
Max Lemaitre: Agreed. This prototype specifically demonstrates how our technology would be implemented in a TV application. We have another prototype which we are working on with Samsung Advanced Institute of Technology which demonstrates the mobile use case (more on this below).
OLED-A: a-Si TFTs tend to suffer from wide variations in the gate voltage, which is a major problem for OLED’ drive TFTs, where the turn-on and turn-off voltages must be precisely controlled.
We do not use a-Si for the drive TFT for these very reasons. Our VOLET device - which can be thought of as a gated-OLED or light emitting triode - is very stable (i.e. negligible Vth shift after 9 months of continuous operation) and allows us to avoid using a-Si for the drive TFT entirely.
OLED-A: The claim that backplanes contribute 20% of the yield loss is absurd, as it tends to be in the 1% range out of the total yield loss of ~20%.
Max Lemaitre: I can’t comment on this with much authority, however in our discussions with panel makers, OLED backplane yields still appear to be a significant issue, especially for IGZO.
OLED-A: The technique would be less expensive and use less masks than LTPS or IGZO but converting an LCD fab to OLEDs needs 3/4 of the OLED capex for the deposition and encapsulation process and more space for a comparable capacity.
Max Lemaitre: Agreed. Our claim is simply that we reduce the total Capex costs as a result of the conversion, and additionally reduce opex cost by simplifying the manufacturing process.
OLED-A: Then there is the matter of LTPO and VRR, given that the cumulative number of OLED panels with LTPO for Samsung and Apple will be 350m+ going forward. And it is likely that new tablets and notebooks will also use LTPO."
Max Lemaitre: Glad you point this out - we completely agree. That is why our other prototype (with Samsung) is based on an IGZO switching-TFT combined with our VOLET. This combination actually allows for even lower frequency operation (<0.2Hz) and requires less than 30% of the mask steps of LTPO.