Design And Research Of Vertical Heterojunction Tunneling Field Effect Transistor

With the continuous shrinking of the feature size of traditional MOSFET devices,the degree of chip integration has gradually improved,and the short-channel effect of the device has become more and more obvious,leading to a significant increase in leakage current when the device is turned off,and the power consumption problem has become more and more serious,which is not conducive to the further improvement of chip integration degree.Due to the influence of hot carrier effect,the subthreshold swing of traditional MOSFETs is higher than 60mV/dec at room temperature.Using NMOS and PMOS tubes can jointly form a complementary MOS structure,that is,CMOS integrated circuit.The series MOSFETs are turned on alternately and turned off at the same time when not in operation.Theoretically,the static power consumption of the circuit is zero.In fact,due to the leakage current,CMOS circuits still have a small amount of static power consumption.The tunneling field effect transistor(TFET)based on the quantum tunneling effect has a sub-threshold slope that can break the theoretical limit of the MOSFET device and has extremely low off-state leakage current.N-type TFET and P-type TFET can also form a complementary TFET(C-TFET)structure.Its on-current is mainly tunneling current,which is not affected by carrier mobility.It is possible to obtain more symmetrical electrical characteristics than CMOS devices without increasing the device size.The main contents of this paper are as follows:Firstly,the application of heterojunction such as SiGe/Si in TFET is discussed.The use of SiGe material in the epitaxial region to form a heteroepitaxial thin layer can effectively reduce the forbidden band width of the epitaxial region,increase the tunneling probability of electrons tunneling from the source region to the epitaxial region,and increase the tunneling current.However,the introduction of narrow bandgap material will directly increase the leakage current.In this design,only the epitaxial region is a narrow bandgap material,and the Ge composition of the SiGe material is low,so it will not cause the degradation of the off-state characteristics.It is proposed that the epitaxial region adopts a gradually doped GEH-TFET structure.By increasing the doping concentration in the epitaxial region near the source,adjusting the tunneling region under low gate voltage,improving the sub-threshold characteristics and shortening the band tunneling distance,which is beneficial to increasing the on-current.Secondly,consider the effects of different structural parameters on the performance of the GEH-TFET.Adjusting the doping concentration in the epitaxial region can improve the electric field which increases the tunneling current of the device.The thickness of the epitaxial region should be controlled at about 4nm to ensure high on-state current and low subthreshold swing.Although the epitaxial region uses a high Ge component can reduce the turn-on voltage of the band tunneling,but in actual process,the Ge content in SiGe cannot be accurately controlled in the ultra-thin epitaxial region of several nanometers.The on-current can be enhanced by increasing the overlap length of the gate and source,but the increase in current will be limited by the series resistance in the intrinsic region.When the overlap length is too long,the leakage current will also increase.Finally,the complementary characteristics of N-type TFET and P-type TFET are analyzed.The N-type and P-type GEH-TFETs can use the same device structure.Only the doping type of the corresponding region needs to be changed to form a complementary TFET similar to CMOS.The flexibility of circuit design is improved and the complexity of the process is reduced.Thus,a heterojunction complementary tunneling FET is realized.