The always-wonderful retro gaming and hardware info site Nicole Express has a great post about the chips that Tengen (a subsidiary of Atari) used in their cartridges! Tengen is a special case among NES developers, in that while a Nintendo licensee they got to use their own mapper, from Namco, but went and manufactured their own ASICs when they split off from Nintendo’s licensing program. The deets are all in the article!
Nicole Express’ archives are well worth a look, which among other items hosts their article on Zaxxon and Future Spy. They have interesting games to play on their itch.io page too! Have I used enough exclamation points yet?!