Chips are fascinating devices indeed!!
This one JW has nicely imaged is an UV erasable EPROM (Erasable Programable Read Only Memory), where intense UV light can erase the entire chip memory. The "hole" in the package has a glass window for passing the UV light.
Later these were replaced by electronic erasable devices, known as EEPROMs. The UV EPROM technology was not generally compatible with other types of chips, so they were separate chips. When the EEPROMs were discovered and developed they could be made compatible with other chip technology and thus ended up "embedded" in our chips today. This is the means of a chip remembering things when unpowered even tho it may not be a dedicated memory chip.
An interesting example of this is with the DACs, like the ones I'm using. DACs are generally considering "Analog" chips, even tho they contain some digital circuitry. Some recent DACs have the ability to be setup to have a specific power up state without additional memory. Most DACs have a unipolar output, but may be required to operate as a bipolar device using 2's Complement coding, where all 0s is the most negative output, all 1s the most positive and the Most Significant Bit (MSB) is 1 and all other bits 0, is the "Zero" output state. Almost all DACs power up in the all bits 0 state, which is a zero output for a unipolar use, but the most negative output for bipolar use. So you have load the DAC with the MSB bit as 1 at power up and block the DAC output until the MSB is latched. All this adds additional circuitry and complexity for bipolar use. With EEPROM on the DAC chip this power up state can be set within the DAC chip and no additional circuitry is required.
Anyway, EEPROM technology has become a very valuable addition to modern chip design. The solid state physics behind the EEPROM is fascinating.
https://en.wikipedia.org/wiki/EEPROM
https://en.wikipedia.org/wiki/Field_ele ... _tunneling
Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
