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Technology Stocks : THREE FIVE SYSTEM (TFS) - up from here? -- Ignore unavailable to you. Want to Upgrade?

To: David W who wrote (1164)	3/29/1998 12:59:00 AM
From: Jim Armstrong	Respond to of 3247

No, there's quite a difference. The LCoS is sort of like removing the glass that contains most of the active circuitry in a regular LCD glass sandwich, and replacing it with the exposed surface of an integrated circuit that performs about the same function. The differences being that the LCoS device is much smaller than the usual LCD, the connections are mostly to the chip (not the glass), and the IC may have any kind of functionality you want, including memory (which is sorta what the usual LCos IC is like, I think). Chip-on-glass is a different sort of thing. In a lot of commercial LCDs, like some Sharp products for example, integrated circuit driver chips are bonded onto the glass along the periphery of the glass. One of the glass glass sheets of the LCD is wider than the other. The LCD's connecting runs are exposed at the edges of the wider glass. The IC driver chips have gold bumps on the chip's contact pads. The pattern of those bumps is such that when the chip is inverted, it can be dropped down on the glass so that the bumps contact the right conductors on the glass. They are bonded there, and sealed with epoxy. In certain displays, that is cheaper than connecting to the glass with some kind of multi-conductor ribbon which then runs to a circuit board containing the drivers. It also means that far fewer connections to the glass are necessary, improving reliability and manufacturability. Ultimately, the holy grail for LCDs is to be able to deposit the drivers right on the glass, instead of bonding ICs to the glass. That would seem to be the obvious way to go, for example, in active-matrix displays (used in laptops) where you are already making thin-film transistors. But for a lot of reasons, that is not being done today, though some companies are saying they are getting closer. So, in a word, chip-on-glass refers to "sticking" driver chips to the periphery of LCD glass. LCoS, on the other hand, incorporates all that addressing circuitry (including the drivers) in a single IC whose surface forms one side of a tiny LCD. LCoS is small, saving on materials. The devices are made with mature IC processes, on parts that are more like normal IC dimensions (unlike laptop displays, for example). The IC can contain any electronic functions you wish to incorporate in the device, and the options are virtually limitless - even to the point of including some interface electronics if economies suggest that's the way to build the chip. Finally, the number of interconnections to the LCoS can be very small compared to other types of LC displays (a very good thing from reliability and manufacturability standpoints). There is one other thing that might be confusing. Kopin uses a unique process for making devices like their Smart Slide. Instead of depositing thin-film transistors at the site of picture element (pixel ), they create an array of transistors in silicon, then transfer them to the LCD glass. That would appear to fit the name "chip-on-glass", but to my knowledge, the term is generally not used to describe the Kopin process. Hope that helps. JimA