Electrical characteristics of Boron-implanted n-channel MOS-transistors for use in logic circuits

In order to obtain enhancement type n-channel MOS transistors in an enhancement-depletion system it is possible to shift the tresbold voltage of the driver transistors to positive values by implanting Boron ions into the channel region of the devices. In this way the advantages of a low bulk doping level are conserved (low parasitic capacitances, low bulk effect ...), while the power dissipation-delay product of the circuits is reduced due to the load which is of the current source type. The Boron implantation changes the uniform doping near the surface and the formulae describing the current-voltage characteristics of the device are altered. we derive adapted formulae starting from the depletion approximation and present an easy way to determine experimentally the parameters governing the current voltage characteristics. For high applied voltages the adapted formulae have the same form as they have for non implanted transistors, but for low voltages, as they are used for low dissipation purposes, a deviation exists, due to the narrowing of the depletion layer as a result of the implantation (See eqs. 6, 9 and 10).