Semiconductor radio frequency switch with body contact

Abstract

The present disclosure relates to a radio frequency (RF) switch that includes multiple body-contacted field effect transistor (FET) elements coupled in series. The FET elements may be formed using a thin-film semiconductor device layer, which is part of a thin-film semiconductor die. Conduction paths between the FET elements through the thin-film semiconductor device layer and through a substrate of the thin-film semiconductor die may be substantially eliminated by using insulating materials. Elimination of the conduction paths allows an RF signal across the RF switch to be divided across the series coupled FET elements, such that each FET element is subjected to only a portion of the RF signal. Further, each FET element is body-contacted and may receive reverse body biasing when the RF switch is in an OFF state, thereby reducing an OFF state drain-to-source capacitance of each FET element.

What is claimed is: 
     
         1 . A method comprising:
 providing an insulating layer;   providing a thin-film semiconductor device layer over the insulating layer;   forming a first body-contacted radio frequency (RF) switch comprising a first plurality of body-contacted field effect transistor (FET) elements coupled in series, such that each body-contacted FET element comprises a source, a drain, and a body formed in at least a part of the thin-film semiconductor device layer, wherein each one of the first plurality of body-contacted FET elements are separated from one another in the thin-film semiconductor device layer by an insulating material; and   providing control circuitry adapted to during an OFF state of the first body-contacted RF switch, provide each body a body bias signal, such that each body and each corresponding source are reverse biased and each body and each corresponding drain are reverse biased to provide reverse body biasing of each corresponding body-contacted FET element.   
     
     
         2 . The method of  claim 1  wherein:
 the control circuitry is further adapted to:
 select the OFF state of the first body-contacted RF switch; and 
 a provide a first body bias control signal, such that each body bias signal is based on the first body bias control signal. 
 
 
     
     
         3 . The method of  claim 2  wherein the first body-contacted RF switch further comprises:
 a first body bias input adapted to receive the first body bias control signal; and 
 a resistor bias network comprising a plurality of body bias resistive elements, such that each of at least some of the plurality of body bias resistive elements is coupled between a body of a corresponding one of the first plurality of body-contacted FET elements and the first body bias input. 
 
     
     
         4 . The method of  claim 3  wherein:
 the control circuitry is further adapted to provide a first switch control signal based on one of the OFF state and an ON state of the first body-contacted RF switch; 
 the first body-contacted RF switch further comprises a first switch connection node and a second switch connection node, such that all of the first plurality of body-contacted FET elements are coupled in series between the first switch connection node and the second switch connection node; 
 during the OFF state, the first body-contacted RF switch has an OFF state impedance between the first switch connection node and the second switch connection node; and 
 during the ON state, the first body-contacted RF switch has an ON state impedance between the first switch connection node and the second switch connection node. 
 
     
     
         5 . The method of  claim 4  wherein:
 the first body-contacted RF switch further comprises a first switch control input adapted to receive the first switch control signal; and 
 each of the first plurality of body-contacted FET elements further comprises a gate, which is coupled to the first switch control input. 
 
     
     
         6 . The method of  claim 5  wherein the resistor bias network further comprises a plurality of gate resistive elements, such that each of at least some of the plurality of gate resistive elements is coupled between the gate of a corresponding one of the first plurality of body-contacted FET elements and the first switch control input. 
     
     
         7 . The method of  claim 6  wherein:
 during the OFF state:
 the first switch connection node has a direct current (DC) voltage equal to about zero volts; 
 the second switch connection node has a DC voltage equal to about zero volts; 
 the first body bias control signal is equal to between about −1 volt DC (VDC) and about −5 VDC; and 
 the first switch control signal is equal to between about −1 VDC and about −5 VDC; and 
 
 during the ON state:
 the first switch connection node has a DC voltage equal to about zero volts; 
 the second switch connection node has a DC voltage equal to about zero volts; 
 the first body bias control signal is equal to about zero volts; and 
 the first switch control signal is equal to between about 1 VDC and about 5 VDC. 
 
 
     
     
         8 . The method of  claim 1  wherein a thickness of the thin-film semiconductor device layer is less than about 500 nanometers. 
     
     
         9 . The method of  claim 8  wherein a thickness of the insulating layer is greater than the thickness of the thin-film semiconductor device layer. 
     
     
         10 . The method of  claim 9  wherein the thickness of the thin-film semiconductor device layer is between about 100 nanometers and about 300 nanometers and the thickness of the insulating layer is between about 200 nanometers and about 1000 nanometers. 
     
     
         11 . The method of  claim 9  further comprising providing a substrate, such that the insulating layer is over the substrate, and a resistivity of the substrate is greater than about 100 ohm-centimeters. 
     
     
         12 . The method of  claim 1  wherein the source of each of the first plurality of body-contacted FET elements and the drain of each of the first plurality of body-contacted FET elements completely traverse a thickness of the thin-film semiconductor device layer. 
     
     
         13 . The method of  claim 12  wherein:
 the source of each of the first plurality of body-contacted FET elements comprises N-type silicon; 
 the drain of each of the first plurality of body-contacted FET elements comprises N-type silicon; and 
 the body of each of the first plurality of body-contacted FET elements comprises P-type silicon. 
 
     
     
         14 . The method of  claim 12  wherein:
 the source of each of the first plurality of body-contacted FET elements comprises P-type silicon; 
 the drain of each of the first plurality of body-contacted FET elements comprises P-type silicon; and 
 the body of each of the first plurality of body-contacted FET elements comprises N-type silicon. 
 
     
     
         15 . The method of  claim 1  wherein the first body-contacted RF switch further comprises a first switch connection node and a second switch connection node, such that:
 all of the first plurality of body-contacted FET elements are coupled in series between the first switch connection node and the second switch connection node; and 
 during the OFF state of the first body-contacted RF switch, an RF signal between the first switch connection node and the second switch connection node is distributed across the first plurality of body-contacted FET elements. 
 
     
     
         16 . The method of  claim 15  wherein a frequency of the RF signal is greater than about 100 megahertz. 
     
     
         17 . The method of  claim 16  wherein during the OFF state of the first body-contacted RF switch, the RF signal between the first switch connection node and the second switch connection node is distributed about equally across the first plurality of body-contacted FET elements. 
     
     
         18 . The method of  claim 1  further comprising providing a substrate wherein:
 the insulating layer is over the substrate; and 
 the insulating layer substantially eliminates conduction paths through the substrate to the other devices. 
 
     
     
         19 . The method of  claim 1  wherein the thin-film semiconductor device layer is partially-depleted and not fully-depleted. 
     
     
         20 . The method of  claim 1  further comprising a second body-contacted RF switch coupled between the first body-contacted RF switch and ground. 
     
     
         21 . The method of  claim 1  wherein the thin-film semiconductor device layer comprises silicon. 
     
     
         22 . The method of  claim 21  further comprising providing a silicon-on-insulator (SOI) substrate, such that:
 the first body-contacted RF switch is an SOI semiconductor device; 
 the insulating layer is an SOI insulating layer, which is over the SOI substrate; and 
 the thin-film semiconductor device layer is a thin-film SOI device layer. 
 
     
     
         23 . The method of  claim 1  wherein the insulating layer provides a substrate. 
     
     
         24 . The method of  claim 23  wherein the insulating layer comprises sapphire. 
     
     
         25 . The method of  claim 1  further comprising providing a plurality of drain-to-source resistive elements, such that each of the plurality of drain-to-source resistive elements is coupled between a corresponding drain and a corresponding source of the first plurality of body-contacted FET elements.