CN103247688B - A kind of graphene field effect pipe of bi-material layers grid linear doping - Google Patents

Abstract

The invention discloses the graphene field effect pipe of a kind of bi-material layers grid linear doping.Based on quantum mechanics unbalance distribution theoretical frame, by self-consistent solution Poisson (Poisson) and Schrodinger (Schr dinger) equation, construct the Transport Model being applicable to graphene field effect pipe, and utilize this model analysis to calculate homogenous material grid and the impact on graphene field effect pipe (GNRFET) electrology characteristic of the bi-material layers dual material gate strategy.By contrasting with using the electrology characteristics such as the output characteristics of bi-material layers grid, transfer characteristic, switch current ratio, find that the graphene field effect pipe of this bi-material layers dual material gate underlap linear doping policy construction has bigger switch current ratio, less subthreshold swing and threshold voltage shift, i.e. show that bi-material layers dual material gate underlap linear doping has more preferable grid-control ability, can effectively suppress short-channel effect, band-to-band-tunneling and hot carrier's effect.

Description

A kind of graphene field effect pipe of bi-material layers grid linear doping

Technical field

The present invention relates to graphene field effect pipe field, particularly with regard to the dual material gate structure of graphene field effect pipe.

Background technology

In recent years, the scientific circles that occur in of Graphene (Graphene) have evoked huge great waves, due to self superior character and quilt It is considered following one of carbon nanomaterial having development potentiality most.Graphene has the highest electron mobility and high conductivity, profit The transistor not only volume made of Graphene is little, low in energy consumption, low to the requirement of working environment, and is readily designed to various knot Structure.But, owing to Graphene is zero band gap material, its Fermi can linearly be distributed, and therefore it is not appropriate for directly applying In transistor.But can by Graphene according to certain orientation cut into the method for band to produce band gap [HAN M Y, OZYILMAZ B,KIM P,et al.Energy band-gap engineering of graphene nanoribbons[J].Phys Rev Lett, 2007,98 (20): 206-805.], it is possible to size (size of band gap and the bar bandwidth of band gap is controlled by the width of band Degree is inversely proportional to).

From the angle of channel engineering, GNR (graphene band) is had more silica-based as the field effect transistor that channel material is made Device performance that metal-oxide-semiconductor is more superior and size reduction prospect, thus graphene band field effect transistor (GNRFET) is considered as structure Build primary element most potential in following nano-electron system.While it is true, due to the band gap of A-GNRs (ArmchairGNR) Different according to the difference of strip width, therefore using different size GNR as the GNRFETs of raceway groove, its application also has very Big difference.Research shows, strip width be 10～15nm GNRFET switch current ratio be only about 10, do not reach completely The requirement of digital circuit, but it has the highest cut-off frequency (cut-off frequency is up to THZ), is therefore very suitable for high frequency/RF In the low gain primary element of module, such as low-noise amplifier [LIN Y M, ALBERTO V G, HAN S J, et al. Wafer-Scale graphene integrated circuit [J] .Science, 2011,332 (6035): 1294-1297.], at present, IBM is Developing the grapheme transistor that the speed of service is the fastest, its cut-off frequency is up to 100GHZ, and has been developed that first is by graphite Integrated circuit [YOON Y, FIORI G, HONG S, the et al.Performance comparison of that former of alkene is made graphene nanoribbon FETs with Schottky contacts and doped reservoirs[J].IEEE Trans Electron Devices,2008,55(9):2314–2323.].On the other hand, in order to obtain enough switch current ratio with applicable digital application, Needing reduction GNR width to increase band gap, existing experimental data shows, arrowband GNRFETs (strip width is about 2 ± 0.5nm) At V_DSDuring=0.5V, ON state current density is about 2000 μ A/ μm, and current on/off ratio reaches 106 [WANGX., OUYANGY, LI X,et al.Room-temperature all-semiconducting sub-10-nm graphene nanoribbon field-effect transistors[J].Phys.Rev.Lett,2008,100(20):206803-206807.]。

Different from the contact type of device source drain terminal electrode according to Graphene, grapheme transistor can be divided into class MOS graphite Alkene nanoribbons field effect transistor (C-GNRFETs) and Schottky barrier graphene nano band field effect transistor (SB-GNRFETs), its Middle C-GNRFETs carries out heavy doping generally by device source drain region so that form Ohmic contact between GNR and source-drain electrode Thus realize the structure of similar MOSFET, and SB-GNRFETs is by intrinsic graphene nano band and metal by directly Electrode contact forms Schottky barrier, and unlike C-GNRFETs, in SB-GNRFETs, the formation of electric current is to carry Stream is tunneled through the Schottky barrier of source and drain end and produces, and the change of grid voltage can cause the change of this potential barrier, Jin Eryin Playing the size of corresponding tunnelling current, owing to there is the effect in electronics and hole in conductor simultaneously, SB-GNRFETs can show bright Aobvious bipolar nature, thus it is substantially reduced device performance.Relative analysis to two class device current characteristics shows, source and drain The C-GNRFET of district's doping has switch current ratio more more preferable device performance than SB-GNRFET, higher and cut-off frequency [YOON Y,FIORI G,HONG S,et al.Performance comparison of graphene nanoribbon FETs with Schottky contacts and doped reservoirs[J].IEEE Trans Electron Devices,2008,55(9): 2314–2323.]。

Summary of the invention

Technical problem: it is an object of the invention to draw because of short-channel effect and other a series of seondary effects for conventional nanoscale device The device performance risen declines problem, it is provided that a kind of bi-material layers dual material gate field effect transistor so that device suppression hot carrier's effect Ability also strengthens.Be obtained in that higher switch current ratio, this make linear doping spin field effect pipe in integrated circuits should Possible with being referred to as.

The present invention under unbalance distribution (NEGF) framework, by self-consistent solution three-dimensional Possion andEquation, The dual material gate graphene field effect pipe electrology characteristic of single grid graphene field effect pipe and bi-material layers is carried out numerical simulation, calculates it The electrology characteristics such as energy level distribution, I-V characteristic, Sub-Threshold Characteristic, switch current ratio, and with the intrinsic of conventional class MOS structure GNRFET compares analysis in terms of suppression hot carrier and short-channel effect.The present invention transports disclosing GNRFET Physical mechanism, improve GNRFET device architecture performance provide theoretical foundation.

Technical scheme: it is an object of the invention to keep acquisition preferably for traditional class MOSFET structure GNRFET High frequency characteristics and switching characteristic while short-channel effect when overcoming device dimensions shrink, it is proposed that a kind of GNRFET's is new Type device architecture.Invention is inspired by dual material gate, introduces the grid structure of bi-material in one structure.Owing to dual material gate is tied Structure can reduce the parasitic capacitance between the direct tunneling leakage at grid edge and grid leak, reduces the electric field of drain terminal simultaneously, reduces leakage current. But being as the reduction of device size, channel length is shorter and shorter, and the impact of short-channel effect becomes serious.And at underlap Region carries out linear doping, and the band-to-band-tunneling thus made reduces, thus reduces off-state current.

The bi-material layers dual material gate field effect transistor of the present invention is a kind of bi-material layers dual material gate structure, and this bi-material layers dual material gate is led by the first Electric metal material and the second conductive metallic material are constituted, wherein with intrinsic grapheme material as conducting channel, conducting channel Fill by dielectric substance oxide layer of the same race respectively between both sides and two gate electrodes, and two gate electrodes formed centered by raceway groove right Claim structure；It is respectively underlap region at the two ends of intrinsic grapheme material, is source region between underlap region and source electrode, Being drain region between underlap region and drain electrode, oxide layer is positioned at outside source region, intrinsic grapheme material, drain region, underlap region Side, the source region of this field effect transistor and drain region are the heavily doped Graphene of N-shaped, and underlap region is linear doping, Nd=N-cx Wherein Nd is the doping content of source-drain area, and x is the length in underlap region, and N is the doping content of the source-drain area started, C For the coefficient of linear change of adulterating, in wherein C > 0, underlap region, the concentration of doping reduces along with the increase of length.

Described bi-material layers dual material gate is the dual material gate that the conductive metallic material that two kinds of work functions are different is constituted, and bi-material is along raceway groove Direction is sequentially distributed, and their work function distribution is as follows: being distributed from the side of close source region to the side near drain region of work function Gradually reduce, it is ensured that the work function near side, drain region is less than the work function near source region side.

Carried out linear doping in underlap region, in underlap region, the concentration of doping reduces along with the increase of length.

Beneficial effect: meaning of the present invention is have employed the structure of a kind of mixing, introduces by two kinds of work functions in GNRFET The dual material gate structure that different materials is constituted, and carry out linear doping in underlap region.And it is based on unbalance distribution Method, under the single grid of relative analysis and bi-material layers dual material gate, the electricity of the graphene field effect pipe under common doping and linear doping is special Property, such as electrology characteristics such as I-V current characteristics, Sub-Threshold Characteristic and switch current ratio, result shows, uses bi-material layers grid line What other single grid structures compared by the graphene field effect pipe of doping has lower off-state current, bigger threshold voltage, higher Switch current ratio, less threshold voltage shift.Show that the device of this structure can preferably suppress DIBL effect, this device is described Part has more preferable grid-control ability, can preferably suppress short-channel effect, reduces band-to-band-tunneling so that device suppression hot carrier The ability of effect also strengthens.

Accompanying drawing explanation

The device architecture model schematic of Fig. 1 present invention.

Wherein have: grid voltage V_G, source voltage V_S, drain voltage V_D, the first material 1 of bi-material layers dual material gate, double material Material dual material gate the second material 2, grid total length L_G, channel length L_G, source, length L in drain region_SAnd L_D, oxide layer Thickness is T_OX1And T_OX2, gate oxide 3, source region 4, raceway groove 5, drain region 6, underlap region 7.

Detailed description of the invention

This field effect transistor generally laminated structure, source electrode and drain electrode are the heavily doped graphene nanobelt of N-shaped；

Be respectively equipped with source electrode, drain electrode at two of graphene field effect pipe, source region, drain region all use the N-type of identical parameters heavily doped Miscellaneous；Graphene field effect pipe mid portion is channel region, and channel region undopes；

In terms of channel direction, grid are positioned at the centre of graphene field effect pipe channel region, and length is equal to channel region length.

Dual material gate is the conductive metallic material composition that two kinds of work functions are different, and bi-material is sequentially distributed along channel direction, they Work function distribution as follows: the work function near source region side is more than the work function of close side, drain region.

Underlap region carries out linear doping.

The spin field effect pipe of the class MOSFET structure of present invention research as shown in drawings, the bi-material layers dual material gate graphite of the present invention Alkene field effect transistor is a kind of double-gate structure, wherein with graphene nanobelt 5 as conducting channel, uses between raceway groove and two gate electrodes Dielectric substance of the same race is filled, and two gate electrodes form symmetrical structure centered by raceway groove；The source region of this field effect transistor and drain region For the heavily doped graphene nanobelt of N-shaped, raceway groove is intrinsic graphene nanobelt.Described double grid is symmetrical about device channel Top-gated and bottom gate, top-gated and bottom gate be made up of the grid of two kinds of different materials respectively, and near source electrode side grid than near drain electrode The work function of the grid of side wants big.The emulation of described field effect transistor is by building tight-binding Hamiltonian under the real space, so After based on unbalance distribution method, self-consistent iteration solves Poisson and Schrodinger equation group, asks for the electricity parameter of system.

Short-channel effect be there will be for nano field-effect tube device, constantly reduce some second-order effects of generation along with device size such as Drain induced barrier reduces (DIBL) problem such as effect and hot carrier's effect, theoretical based on quantum mechanics unbalance distribution (NEGF) Framework, under the conditions of open boundary, by self-consistent solution Poisson and Schrodinger equation, constructs applicable bi-material layers dual material gate graphite The Transport Model of alkene field effect transistor, and utilize this model analysis to use the impact on field effect transistor electrology characteristic of the dual material gate strategy.Always Seeing on body, this dual material gate Policy model has the feature that

A. it is the dual material gate structure of a kind of bi-material layers, and wherein intrinsic graphene nanobelt is as conducting channel, raceway groove and two grid Fill with dielectric substance of the same race between electrode, and two gate electrodes form symmetrical structure centered by raceway groove.

B. the source/drain region of device all uses N-shaped heavy doping Graphene, and raceway groove uses intrinsic Graphene.

C. the calculating of model is to utilize NEGF method, under the conditions of open boundary, and self-consistent solution Poisson's equation and Schrodinger equation.

The calculating of model is to utilize unbalance distribution (NEGF) method, under the conditions of open boundary, self-consistent solution Poisson and Xue Determine straightforward words equation.Detailed process is a given original trench electromotive force, utilizes NEGF Equation for Calculating to go out its charge density, then by electricity Lotus density substitutes into Poisson's equation and solves the electrostatic potential in silicon raceway groove, is again substituted in NEGF equation by the electromotive force tried to achieve the most again Calculating, so iterating until obtaining self-consistent solution.

Charge density and electromotive force are carried out from being in harmony calculating by our model based on GNRFET quantum model.And charge density can be by Unbalance distribution method obtains.First the sluggish Green of this device is obtained according to model:

G(E)=[(E+iη⁺)I-H_D-Σ_D-Σ_S]^-1 (1)

Wherein, η⁺Representing a positive dimensionless, E is energy, H_DRepresent the most adjacent approximation of graphene nano banded zone The Hamiltonian of lower electronics, Σ_SAnd Σ_DRepresent source electrode and the self energy item of drain region contribution in device respectively, surface lattice can be passed through The alternative manner of woods function is obtained.After obtaining Green's function, in device the hole of any position and electron density all can by under Formula is obtained

$n\left(x\right)={\∫}_{E_I}^{+\∞}\mathrm{dE}\[G{\mathrm{\Γ}}_S{G}^{+}f(E-E_{\mathrm{FS}})+G{\mathrm{\Γ}}_D{G}^{+}f(E-E_{\mathrm{FD}})\]$

(2)

$p\left(x\right)={\∫}_{-\∞}^{E_I}\mathrm{dE}\{G{\mathrm{\Γ}}_S{G}^{+}\[1-f(E-E_{\mathrm{FS}})\]+G{\mathrm{\Γ}}_D{G}^{+}\[1-f(E-E_{\mathrm{FD}})\]\}$

Wherein E_IRepresent the fermi level in GNR region, E_FS(D)Fermi level for source (leakage) region.

After obtaining carrier density, substituted into and the Solving Three-Dimensional poisson Equation of device is carried out self-consistent solution, the three-dimensional Poisson of device Equation polar coordinate representation can be written as

${\▿}^{2}U(x,z)=-\frac{e}{\mathrm{\ϵ}}\mathrm{\ρ}(x,z)---\left(3\right)$

Wherein U represents that electrostatic potential, ε represent that dielectric constant, ρ represent that net charge is distributed.

Electromotive force V at grid and graphene nano ribbon contacts is then determined by the Dirichlet boundary condition in device, eV=eV_g +Φ_GNR–Φ_g, wherein V_gRepresent grid voltage, Φ_GNRAnd Φ_gRepresent graphene nano band and the work function of grid respectively. At source electrode, drain contact areas and the boundary condition not having other borderline region contacted to use Neumann type with electrode, I.e. on border, the normal component of its potential gradient is 0, so could meet the electroneutrality condition of built-in field in device.

Landauer-B ü ttiker formula is finally utilized to try to achieve from source electrode to the channel current of drain electrode:

$I=\frac{4e}{h}\∫\mathrm{dET}\left(E\right)\[f(E-E_{\mathrm{FS}})-f(E-E_{\mathrm{FD}})\]---\left(4\right)$

Wherein e represents that electron charge, h represent planck constant, f (E-E_FS(D)) represent Fermi potential distribution function, E_FSRepresent source electrode Fermi level, E_FDRepresent that drain electrode Fermi can carry, T [E]=Trace [Γ G Γ G⁺], represent the tunnelling coefficient of carrier in device.

The output characteristics of 1 bi-material layers grid line doped field effect pipe

Used the I-V current characteristics of the graphene field effect pipe of different grid strategy by contrast, find under identical grid voltage, use double The graphene field effect pipe output electric current of material dual material gate structure is less, and the output of the graphene field effect pipe of conventional single grid material Electric current is relatively big, and its conductance is greater than the former.Under the graphene field effect pipe of single grid material, short-channel effect is it is obvious that also And current ratio bi-material layers dual material gate graphene field effect Guan Dou great.When the length of raceway groove is reduced to nano level time, source-drain electrode The shared in channels ratio of depletion region will increase, and the quantity of electric charge of the inversion layer that face is formed reduces under the gate, simultaneously in substrate Depletion region make threshold voltage increase along the electric charge of raceway groove.In order to avoid these problems caused by short channel it is necessary to reduce raceway groove Electric field, the especially electric field of drain terminal, device is carried out bi-material layers grid and improves and reduce short-channel effect and shadow that DIBL brings Ring.

The Sub-Threshold Characteristic of the graphene field effect pipe of 2 bi-material layers grid linear dopings

In order to study the different grid structure strategy impact on graphene field effect pipe performance, probe into the novel bi-material layers that the present invention proposes Dual material gate structure is relative to other structures improvement degree to device performance, to the graphene field effect pipe using different grid structures Sub-Threshold Characteristic has been made to analyze, and sub-threshold slope characterizes the subthreshold region gate voltage control ability to channel current.Comparing result shows The graphene field effect pipe of single grid structure, its sub threshold slope characteristic is the worst, and the graphene field effect of bi-material layers dual material gate Pipe, has optimal sub-threshold slope, reflects that the grid-control ability of this grid structure is substantially better than other structures.DIBL effect refers to When device channel length reduces, and drain voltage increases so that the depletion region of source and drain terminal is very close to, the field intensity that drain region sends A part in line terminates in raceway groove by depletion region, causes source barrier height to reduce, causes threshold voltage to reduce.By right Than single grid structure graphene field effect pipe with use the threshold voltage shift of graphene field effect pipe of bi-material layers dual material gate strategy, Finding when increasing to 0.5V from drain terminal voltage from 0V, common threshold voltage falls 40mV, and bi-material layers dual material gate structure Only fall 10mV, illustrate that bi-material layers dual material gate structure can preferably suppress the ability of DIBL effect than single grid structure.

Claims (1)

1. a bi-material layers dual material gate field effect transistor, it is characterised in that this field effect transistor is a kind of bi-material layers dual material gate structure, this pair Material dual material gate is made up of the first conductive metallic material (1) and the second conductive metallic material (2), wherein uses intrinsic graphite Alkene material (5) is as conducting channel, the both sides of conducting channel and two gate electrode (V_GDielectric substance of the same race is used respectively between) Oxide layer (3) is filled, and two gate electrodes form symmetrical structure centered by raceway groove；Two ends in intrinsic grapheme material (5) It is respectively underlap region (7), is source region (4) between underlap region (7) and source electrode (VS), underlap region (7) With drain electrode (V_DDrain region (6) between), oxide layer (3) be positioned at source region (4), intrinsic grapheme material (5), drain region (6), The outside in underlap region (7), the source region (4) of this field effect transistor and drain region (6) are the heavily doped Graphene of N-shaped, underlap Region (7) is linear doping, and Nd=N-cx wherein Nd is the doping content of source-drain area, and x is the length in underlap region, N is the doping content of the source-drain area started, and C is the coefficient of doping linear change, adulterates in wherein C > 0, underlap region Concentration reduce along with the increase of length；

Described bi-material layers dual material gate is the dual material gate that the conductive metallic material that two kinds of work functions are different is constituted, and bi-material is along raceway groove Direction is sequentially distributed, and their work function distribution is as follows: the distribution of work function near the side of source region (4) to close drain region (6) Side gradually reduce, it is ensured that the work function near drain region (6) side is less than near the work function of source region (4) side.