Shares in Micron Technology Inc fell in heavy trading yesterday after the chipmaker said its three top executives will resign over the next month for personal reasons – sounds as if they want to set up a new company to exploit something developed at the Boise, Idaho firm: Micron shares were off $1.75 at $37.75 at mid-morning on the New York Stock Exchange, where it was among the most active issues; one broker noted that Steve Appleton, who will become chairman and chief executive, has in effect been running the company for the past several years, and that the new managers are strong people and business trends remain very strong; Tyler Lowrey will become vice-chairman, director and chief technical officer; and Bill Stover will be vice-president, finance, treasurer and chief financial officer.