Method of making a low parasitic resistor on ultrathin silicon on insulator

A method for forming a diffused resistor and a MOSFET in a thin semiconductor layer, the method comprising the steps of:

• providing an insulating substrate;
• forming the thin semiconductor layer on the insulating substrate wherein the thin semiconductor layer has a maximum fixed charge density of no more than about 5.times.10.sup.11 cm.sup.-2 ;
• forming a first electrically isolated portion of the thin semiconductor layer and a second electrically isolated portion of the thin semiconductor layer wherein at least the first electrically isolated portion has the maximum fixed charge density of no more than about 5.times.10.sup.11 cm.sup.-2 ;
• providing any resistor implants in a resistive region of the first electrically isolated portion of the thin semiconductor layer wherein the resistor implants are for setting a resistance of the diffused resistor;
• preventing any implants other than the any resistor implants from being provided in the resistive region;
• forming in the first electrically isolated portion of the thin semiconductor layer a first contact region and a second contact region wherein the first contact region is electrically coupled to the resistive region by being contiguous with a first portion of the resistive region and wherein the second contact region is electrically coupled to the resistive region by being contiguous with a second portion of the resistive region;
• forming a MOSFET in the second electrically isolated portion of the thin semiconductor layer.