 Hello everyone. Today I'm giving a presentation on how to successfully integrate a cover glass onto our new product, the VL53L5CX. So when you put a cover glass on top of a time-of-flight device, the issue that occurs is crosstalk. So you might ask, what is crosstalk? Well below is a diagram showing exactly how we want the device to operate and what we don't want to operate. So the green line is showing exactly how the time-of-flight works. We have a laser emitter, the photon goes out, hits a target, comes back, and we get a nice reading. The issue with a cover glass is a photon can hit the cover glass, bounce back to our device multiple times, and come back and finally hit our receiver, giving you a very short distance as far as the total range. We don't want that to happen. But the nice thing about our device is we can characterize what the crosstalk is, measure it, and then remove it when doing final measurements. So in this presentation, what we're trying to show is the best properties of the cover glass to give us the least amount of crosstalk. But on top of that, at the very end, we're going to do a calibration. So whatever crosstalk is remaining, we can remove it. The first step for successfully integrating a cover glass is to obtain one of our application eval boards with the time-of-flight sensor that you're going to be using for your application. And from this, you can actually do a full calibration on a cover glass. So this slide is showing the eval oation kit for the VL53L5CX. When you get this, it's going to have the expansion board, which is the big blue board. On top of that, you need an STM32 nuclear board, which is going to actually give the communication to our sensor to configure it and operate it. Also included in our eval kit is we get some cover spacers. These spacers basically let you adjust the height of the cover glass from the top of our device. Obviously, it is impossible to have a cover glass touching our device because in a manufacturing environment, you can't get those precise of tolerances. So we give some different thicknesses of spacers so you can put the cover glass to match whatever your product will be. We also give an example cover glass that has an IR encoding on it. But obviously, the perfect test is if you can use the actual cover glass of your final product with the spacers to match the space in your final product, then you can actually measure the crosstalk for this device. The next step is to pick the cover glass that fits your application. In this, many different criteria are needed and we're going to go over the criteria that will give you the best performance with as little crosstalk as possible. Before picking a cover glass, many people ask, why do we need a cover glass in the first place? The main reason for this is to protect our device. Our device is not hermetically sealed. So if you want to ensure that no dust gets inside our part or water or any sort of contaminants that could interfere with the long-term performance of our board, a cover glass is needed to ensure protection of our device. In choosing a cover glass, the main things we want to do is minimize the haze. A haze on a cover glass will actually take the photons hitting it and spread it out in all directions. What we want is that the transmitter of our device goes cleanly through the cover glass and hits the target and comes back with no interference. To do this, you want the cover glass to have no structural defects. We want it as flat as possible. No anti-reflectance coatings on there and be very careful on choosing the anti-fingerprint coating that you put on the cover glass. Some anti-fingerprint materials can actually increase the crosstalk dramatically. So we want it to be as low a crosstalk as possible. One thing to note is if you put an IR ring that basically lets all the 940 nanometer laser to go through the glass and blocks out the visible light, you can see two pictures here, one where we show a rough ink and one where we show a smooth ink. Essentially, we do not want the surface to look rough when looking through a microscope. You want it to be as smooth as possible and this will reduce the crosstalk as much as possible. One other thing is the cover glass transmission. We want as much of the IR to go through as possible. So in our guidelines, we recommend that your transmittance of 940 nanometer is greater than 90 percent. Sometimes that can't be helped that sometimes for your application, you might have a lower reflectance or I mean lower transmittance. But just note that the lower the transmittance of the glass, the more the performance of the part will be reduced. For mechanical requirements, the closer the cover glass is to our part, the less crosstalk it will have. So we recommend having an air gap of 0.5 millimeters or less. Obviously, if you can have it touching, it's going to give you the best performance, but obviously in a manufacturing environment, that is not always possible. The second thing is the actual thickness of the cover glass. The photons can bounce within the cover glass, so the thinner it is, the less crosstalk you're going to have. So we recommend a 1 millimeter thickness of a cover glass will give you decent performance yet give you some good strength. This is showing basically a side view of how the cover glass looks on our BL5305 device. The IR coating, we want it to be on the bottom side of the glass, not the top, to help reduce the crosstalk as much as possible. And another thing to consider is tilt. On the bottom, we're showing how the device might be tilted with the cover glass. What we recommend is that the cover glass is as parallel to our device as possible. Anytime you put a slight slant on it, it will definitely increase the crosstalk in the final application. Another thing to consider to reduce crosstalk is a gasket. So a gasket can be made of foam or rubber, and it's placed on top of our device. You put hole openings in the gasket. So essentially the gasket is touching the top of our part and it's touching the bottom of the glass. And essentially the photons are then guided through these holes to leave the device and come back only through these holes, by which we're reducing crosstalk as crosstalk can be caused from the photons coming out of our device, hitting the glass and bouncing back to our device. By having the gasket in between the transmitter and the receiver, this can reduce crosstalk dramatically. This also helps in situations if you need to have an air gap more than 0.5 millimeters. The last step is to actually do a crosstalk calibration. ST provides a software that will do the calibration, so this can be done in a production environment, or in a laboratory environment, whatever is needed for your typical application. This slide is showing the actual results of crosstalk calibration on our VL53L5. There's actually two components that we have in our calibration. The first is the signature or the shape of how the photons are coming back to our device. And the second one is the actual amount of crosstalk in each of the 64 zones of our part. With this you can see that the crosstalk is as high as 45 kilofotons per second and as low as 10 kilofotons per second. So with knowing both of these information, we can then know that this crosstalk is always coming because of the cover glass, and we can subtract this out from each individual histogram on the part, giving you the perfect results every time you do arranging. So in conclusion, when selecting the cover glass for your device, the main considerations that we want you to choose from is that the cover glass is very flat, has a very smooth surface, especially when looking under a microscope. This will ensure that your haze is as low as possible. We want an optical transmission to be greater than 90%. We want the transparency of this 90% to be at 940 nanometers, which is the transmission of the laser on our VL53L5CX. Some good examples is a glass and acrylic, a PMMA or a polycarbonate material. The cover glass material from glass or plastic, we don't want to have an anti-reflectance coating at all. We want the clean cover glass, so no dirt on the cover glass. If dirt is added afterwards, such as dust from sitting from a long period of time, this will add crosstalk over time and a new calibration can be needed, or you could apply a higher crosstalk value for each zone to compensate for any dust or dirt that is accumulating over time. For the mechanical constraints, we want the air gap to be as small as possible. We want the glass to be parallel with our device, and the thinner the glass, the better, where we recommend a 1mm cover glass thickness. If you have any questions, please do not hesitate to go to our website at www.st.com.timeoflight, or contact your local ST sales representative.