Thermal characteristics of the thermal gradient chip. (A) When a single island is heated on an unfinned chip, the temperatures of surrounding unheated islands are affected (simulation by mathematical model). (B) A plot of temperature versus position forA clearly shows isothermal islands, and the steep temperature drops between them in the insulating membrane. (C) When four islands surrounding an unheated island are heated (right), their combined effect on the temperature of the central island is much greater than when a single island is heated (left; actual thermal image of unfinned chip; see text for details). (D) The voltage-versus-temperature characteristics of the thermal sensor are fairly linear over the temperature range of interest for hybridization.