Method for improving transconductance and characteristic frequency of AlGaN / GaN heterojunction field effect transistor based on device structure optimization

Abstract

This invention relates to a method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization, belonging to the field of transistor device research technology. Traditional methods for improving transconductance and characteristic frequency are complex in fabrication, require stringent experimental conditions, and have reached the physical limits of GaN materials. This invention, to a certain extent, only requires optimizing the device structure and fabricating the L… GS / L G and L GD / L G AlGaN / GaN HFETs with larger ratios, and the fabrication of L G Smaller AlGaN / GaN HFETs enhance polarized Coulomb field scattering, thereby improving the gate voltage's ability to modulate electron velocity, or fabricate L... GS and L G Smaller AlGaN / GaN HFETs enhance the electron velocity in the channel, thus achieving the same effect of increasing the transconductance and characteristic frequency of AlGaN / GaN HFETs. They are simple, direct, and highly operable.

Description

Technical Field

[0001] This invention relates to a method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization, belonging to the field of transistor device research technology. Background Technology

[0002] AlGaN / GaN heterojunction field-effect transistors (HFETs) are important representatives of high-frequency devices and power electronic devices. Among them, transconductance (g) is... m ) is the drain current (I ds ) for gate-source voltage (V gs The derivative of the characteristic frequency (f) reflects the gate's control over the channel current, which is crucial for the output current, operating frequency, and power characteristics of AlGaN / GaN HFET devices. T ) is the current gain (h) 21 The frequency at which the frequency drops to 1 is crucial for the RF characteristics of AlGaN / GaN HFET devices.

[0003] Therefore, this study establishes device structure optimization rules to improve the performance of AlGaN / GaN HFET devices. m with f T This approach is both urgent and necessary. Summary of the Invention

[0004] In AlGaN / GaN HFETs, transconductance g m The expression is as follows:

[0005]

[0006] Where, n s It is the channel electron density, v e It is the channel electron velocity, and e is the charge. It is the modulation of the channel electron density by the gate-source voltage. This refers to the modulation of the channel electron velocity by the gate-source voltage. Previous methods for improving the transconductance of AlGaN / GaN HFET devices mainly involved increasing n... s and These methods include improvements to multi-channel AlGaN / GaN NFET processes. s Furthermore, AlGaN / GaN FinFET processes enhance gate control capabilities. These methods are complex and demanding, and have reached the physical limits of GaN materials.

[0007] Recent experiments have revealed a significant modulation effect of gate voltage on channel electron velocity. To further expand the application prospects of AlGaN / GaN HFETs in microwave power circuits and continuously improve their electrical performance, this invention provides a method for enhancing the modulation effect of gate voltage on electron velocity and increasing channel electron velocity through device structure optimization, thereby improving the transconductance g of AlGaN / GaN HFET devices. m With characteristic frequency f T .

[0008] The present invention adopts the following technical solution:

[0009] A method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization, by enhancing... and v e To enhance the transconductance of AlGaN / GaN HFETs;

[0010] As can be seen from formula (1), in order to significantly improve the transconductance of AlGaN / GaN HFET, It is an important physical parameter. However, it has not been studied in depth in previous literature. The underlying physical mechanism, as proposed in this invention, is to effectively enhance polarized Coulomb field scattering. This improves the transconductance and characteristic frequency of AlGaN / GaN HFETs.

[0011]

[0012] Where C gs It is the gate-source capacitance, C gd It is the gate-drain capacitance, C gs and C gd It is divided into two parts, one part being the intrinsic capacitance C gs_int C gd_int The other part is the parasitic capacitance C. gs_ext C gd_ext ; t total It is the total transit time, τ t It is the transit time under the fence, τ par It is the transit time of the parasitic effect, τ ext It is the charge transit time of the parasitic capacitance; g0 is the conductance, R s It is the gate-source resistance, R d It is the gate-drain resistance, L G It is the grid length, f T It is the characteristic frequency;

[0013] Using formula (2), we can increase the characteristic frequency f. T It needs to be improved Improve gm Reduce the gate-source capacitance and gate-drain capacitance, and reduce the gate-source resistance and gate-drain resistance;

[0014] Polarized Coulomb field scattering originates from the uneven distribution of polarization charges in the AlGaN barrier layer of an AlGaN / GaN HFET. Due to the gate and drain bias applied to the AlGaN / GaN HFET, the inverse piezoelectric effect occurs, causing the strain of the AlGaN barrier layer under the gate to differ from that in the gate-source and gate-drain regions. The difference between the polarization charge density under the gate and the polarization charge density in the gate-source and gate-drain regions is defined as the additional polarization charge density. This additional polarization charge density generates a scattering potential, which scatters channel electrons. In the strong-field transport of AlGaN / GaN HFETs, polarized Coulomb field scattering plays a dominant role. As the gate voltage decreases (the gate voltage increases negatively), the additional polarization charge density increases, enhancing polarized Coulomb field scattering. This leads to a decrease in velocity as the gate voltage decreases, thus generating positive polarization charge density. Therefore, effective enhancement can be achieved by enhancing polarized Coulomb field scattering.

[0015] This invention effectively enhances polarized Coulomb field scattering. This improves the transconductance and characteristic frequency of AlGaN / GaN HFETs.

[0016] Preferably, the polarized Coulomb scattering potential experienced by electrons in the channel can be expressed as:

[0017]

[0018] Where V(x, y, z) is the polarized Coulomb field scattering potential, ε0 is the vacuum permittivity, and ε s L is the relative permittivity of the barrier layer. G L is the gate length. GS L is the gate-source distance. GD ρ is the gate-drain spacing, W is the gate width, e is the charge amount, x is the channel along the gate length, y is the channel along the gate width, z is the channel along the longitudinal widening direction, x′ is the position of the additional polarization charge in the x direction, and y′ is the position of the additional polarization charge in the y direction; ρ0 is the polarization charge density in the gate-source region and the gate-drain region; the channel is divided into several grids, each grid corresponding to a coordinate (x1, x2) and a polarization charge density ρ2, ρ1 is the polarization charge density at the leftmost end under the gate, and ρ3 is the polarization charge density at the rightmost end under the gate;

[0019] From the integration interval and integral terms of formula (3), it can be seen that the scattering intensity of the polarized Coulomb field is related to L GS / L G and L GD / LG The ratio is directly proportional when L GS / L G and L GD / L G As the ratio increases, polarized Coulomb field scattering is enhanced;

[0020] The method to optimize the transconductance of AlGaN / GaN HFETs is to increase L GS / L G and L GD / L G The ratio can effectively enhance polarized Coulomb field scattering, thereby increasing... Effectively improve the g of AlGaN / GaN HFET m This invention designs L GS / L G and L GD / L G Larger AlGaN / GaN HFET device structures can increase the amount of additional polarization charge or bring the additional polarization charge closer to the gate electrons, thereby effectively enhancing polarization Coulomb field scattering and improving the g-factor of AlGaN / GaN HFETs. m .

[0021] Preferably, by reducing the gate length L G This brings the additional polarization charge closer to the electrons under the grating, thereby effectively enhancing the polarization Coulomb field scattering and increasing its intensity. Improving the g of AlGaN / GaN HFET m with f T This invention designs L G Smaller device structures can also effectively increase the average electric field of the channel, thereby increasing the electron velocity in the channel. According to formula (1), the increase in electron velocity can effectively increase the g of AlGaN / GaN HFET. m Furthermore, the increased channel electron velocity reduces the electron transit time under the gate, significantly improving the f-value of AlGaN / GaN HFETs. T .

[0022] Preferably, the formula E = V / L is used, where V is the voltage applied to the device and L is the channel distance (here, L can be L). GS This effectively reduces the gate-source distance L. GS This can increase the average electric field E in the channel, thereby increasing the channel electron velocity and improving the g-factor of AlGaN / GaN HFETs. m with f T (reducing L) GS The electric field below the gate can be increased. A larger electric field can increase the electron velocity, and this increased electron velocity will lead to a larger g. mThe increased speed can offset the effect of L GS Decrease, resulting in L GS / L G Smaller, reducing g caused by polarized Coulomb field scattering m Therefore, the gate-source distance L is reduced here. GS This can improve the g of AlGaN / GaNHFET. m with f T ).

[0023] This invention designs L GS A smaller device structure can also effectively reduce the gate-source resistance R. S Decrease R S C gs Time constant (because) Decrease L GS It can effectively reduce R S C gs (Time constant), thereby improving the f of AlGaN / GaN HFET T .

[0024] For any details not covered in this invention, please refer to the prior art.

[0025] The beneficial effects of this invention are as follows:

[0026] Existing processes for improving the transconductance and characteristic frequency of AlGaN / GaN HFETs are complex, require stringent experimental conditions, and have reached the theoretical limits of GaN materials. This invention, to a certain extent, only requires optimizing the device structure and fabricating L... GS / L G and L GD / L G AlGaN / GaN HFETs with larger ratios, and the fabrication of L G Smaller AlGaN / GaN HFETs enhance polarized Coulomb field scattering, thereby improving the gate voltage's ability to modulate electron velocity, or fabricate L... GS and L G Smaller AlGaN / GaN HFETs enhance the electron velocity in the channel, thus achieving the same effect of increasing the transconductance and characteristic frequency of AlGaN / GaN HFETs. They are simple, direct, and highly operable. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0028] Figure 1 This is a schematic diagram of the channel electron velocity for samples with different gate lengths under different gate voltages.

[0029] Figure 2 g for devices with different gate lengths m With V gs A schematic diagram of the functional relationship.

[0030] Figure 3 f for three devices with different gate lengths T With V gs The functional relationship. Detailed implementation method:

[0031] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0032] Example 1

[0033] A method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization. In AlGaN / GaN HFETs, the transconductance g m The expression is as follows:

[0034]

[0035] Where, n s It is the channel electron density, v e It is the channel electron velocity, and e is the charge. It is the modulation of the channel electron density by the gate-source voltage. It is the modulation of the channel electron velocity by the gate-source voltage.

[0036] According to formula (1), to enhance the transconductance (g) of AlGaN / GaN HFET... m ), can be enhanced and v e To improve the transconductance g of AlGaN / GaN HFET devices m With characteristic frequency f T .

[0037]

[0038] Where C gs It is the gate-source capacitance, C gd It is the gate-drain capacitance, C gs and C gd It is divided into two parts, one part being the intrinsic capacitance C gs_int C gd_int The other part is the parasitic capacitance C. gs_ext C gd_ext ;t total It is the total transit time, τ t It is the transit time under the fence, τ par It is the transit time of the parasitic effect, τ ext It is the charge transit time of the parasitic capacitance; g0 is the conductance, R s It is the gate-source resistance, R d It is the gate-drain resistance, L G It is the grid length, f T It is the characteristic frequency;

[0039] Using formula (2), we can increase the characteristic frequency f. T It needs to be improved Improve g m Furthermore, it is necessary to reduce the gate-source capacitance and gate-drain capacitance, as well as the gate-source resistance and gate-drain resistance;

[0040] Polarized Coulomb field scattering originates from the uneven distribution of polarization charges in the AlGaN barrier layer of an AlGaN / GaN HFET. Due to the gate and drain bias applied to the AlGaN / GaN HFET, the inverse piezoelectric effect occurs, causing the strain of the AlGaN barrier layer under the gate to differ from that in the gate-source and gate-drain regions. The difference between the polarization charge density under the gate and the polarization charge density in the gate-source and gate-drain regions is defined as the additional polarization charge density. This additional polarization charge density generates a scattering potential, which scatters channel electrons. In the strong-field transport of AlGaN / GaN HFETs, polarized Coulomb field scattering plays a dominant role. As the gate voltage decreases (the gate voltage increases negatively), the additional polarization charge density increases, enhancing polarized Coulomb field scattering. This leads to a decrease in velocity as the gate voltage decreases, thus generating positive polarization charge density. Therefore, effective enhancement can be achieved by enhancing polarized Coulomb field scattering.

[0041] Enhanced polarized Coulomb field scattering can effectively enhance... This improves the transconductance and characteristic frequency of AlGaN / GaN HFETs.

[0042] The polarized Coulomb scattering potential experienced by electrons in the channel can be expressed as:

[0043]

[0044] Where V(x, y, z) is the polarized Coulomb field scattering potential, ε0 is the vacuum permittivity, and ε s L is the relative permittivity of the barrier layer. G L is the gate length. GS L is the gate-source distance. GDρ is the gate-drain spacing, W is the gate width, e is the charge amount, x is the channel along the gate length, y is the channel along the gate width, z is the channel along the longitudinal widening direction, x′ is the position of the additional polarization charge in the x direction, and y′ is the position of the additional polarization charge in the y direction; ρ0 is the polarization charge density in the gate-source region and the gate-drain region; the channel is divided into several grids, each grid corresponding to a coordinate (x1, x2) and a polarization charge density ρ2, ρ1 is the polarization charge density at the leftmost end under the gate, and ρ3 is the polarization charge density at the rightmost end under the gate;

[0045] From the integration interval and integral terms of formula (3), it can be seen that the scattering intensity of the polarized Coulomb field is related to L GS / L G and L GD / L G The ratio is directly proportional when L GS / L G and L GD / L G As the ratio increases, polarized Coulomb field scattering is enhanced;

[0046] The method to optimize the transconductance of AlGaN / GaN HFETs is to increase L GS / L G and L GD / L G The ratio, i.e., the design L GS / L G and L GD / L G A larger ratio of AlGaN / GaN HFET enhances polarized Coulomb field scattering, thereby increasing... Effectively improve the g of AlGaN / GaN HFET m .

[0047] Example 2:

[0048] A method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization is described in Example 1. The difference lies in the specific methods for enhancing polarized Coulomb field scattering and increasing channel electron velocity: designing the gate length L... G Smaller AlGaN / GaN HFETs. This is achieved by reducing the gate length L. G This brings the additional polarization charge closer to the electrons under the grating, thereby effectively enhancing the polarization Coulomb field scattering and increasing its intensity. Improving the g of AlGaN / GaN HFET m with f T .

[0049] Example 3:

[0050] As described in Example 1, a method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization is proposed. The difference lies in the specific method for increasing the channel electron velocity: designing an AlGaN / GaN HFET with a smaller gate-source spacing (LGS), thereby increasing the channel electron velocity and improving the transconductance and characteristic frequency of the AlGaN / GaN HFET. m with f T .

[0051] Application example:

[0052] As described in Example 2, the method for improving the transconductance and characteristic frequency of AlGaN / GaN HFETs was used to fabricate three gate length L... G AlGaN / GaN HFETs with diameters of 0.25μm, 0.35μm, and 0.5μm respectively, all have a gate-source pitch and a gate-drain pitch of 1μm, and a gate width of 40μm. (Except for the gate length L...) G Apart from that, the device structure, material structure, and process steps are consistent.

[0053] The channel electron velocities of three samples with different gate lengths under different gate voltages were extracted using small-signal S-parameter testing (a common method for testing the high-frequency characteristics of semiconductor devices) and formula (2). Figure 1 As shown. From Figure 1 As can be seen from this, devices with short gates and long grids have relatively high electron velocities. And in V... gs <-1.5V, comparing three samples, short-gate-length AlGaN / GaN HFET The effect is relatively large. When the gate length decreases, under the same drain-source bias, the channel electric field of a short-gate device increases significantly, thereby increasing the electron velocity and effectively improving g. m Furthermore, it reduces the transit time under the gate, thereby improving f. T According to formula (3), the additional polarization charge of a short-gate long device is closer to the channel electrons, which greatly enhances the scattering of the polarization Coulomb field, thereby increasing the... It also effectively improved g m This improved f T .

[0054] To verify the effectiveness of the method described in this invention, transfer characteristic curves of the three devices were tested using a semiconductor parameter analyzer (I... ds -V gs By differentiating the gate-source voltage once, g was obtained for three devices with different gate lengths. m With V gs Functional relationships, such as Figure 2 As shown. The f-parameters of three devices with different gate lengths were obtained through small-signal S-parameter tests under different gate voltages.T With V gs Functional relationships, such as Figure 3 As shown. Figure 2 This can explain the g of short-gate-length AlGaN / GaN HFETs. m It is significantly longer than the gate length of a long AlGaN / GaN HFET. Figure 3 This can explain the f of short-gate AlGaN / GaN HFETs. T The f value is significantly greater than that of long gate length AlGaN / GaNHFET. T This also demonstrates from an experimental perspective that reducing the grating length enhances polarized Coulomb field scattering, thereby increasing... Furthermore, by increasing the electric field under the gate and enhancing the electron velocity under the gate, the g-factor of AlGaN / GaN HFETs can be effectively improved. m with f T .

[0055] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization, characterized in that, In AlGaN / GaN HFETs, transconductance g m The expression is as follows: Where, n s It is the channel electron density, v e It is the channel electron velocity, and e is the charge. It is the modulation of the channel electron density by the gate-source voltage. It is the modulation of the channel electron velocity by the gate-source voltage, through enhancement and v e To enhance the transconductance of AlGaN / GaN HFETs; Where C gs It is the gate-source capacitance, C gd It is the gate-drain capacitance, C gs and C gd It is divided into two parts, one part being the intrinsic capacitance C gs_int C gd_int The other part is the parasitic capacitance C. gs_ext C gd_ext ; t total It is the total transit time, τ t It is the transit time under the fence, τ par It is the transit time of the parasitic effect, τ ext It is the charge transit time of the parasitic capacitance; g0 is the conductance, R s It is the gate-source resistance, R d It is the gate-drain resistance, L G It is the grid length, f T It is the characteristic frequency; Using formula (2), we can increase the characteristic frequency f. T It needs to be improved Improve g m Reduce the gate-source capacitance and gate-drain capacitance, and reduce the gate-source resistance and gate-drain resistance; By enhancing polarized Coulomb field scattering, it is possible to effectively enhance... This improves the transconductance and characteristic frequency of AlGaN / GaN HFETs.

2. The method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization according to claim 1, characterized in that, The polarized Coulomb scattering potential experienced by electrons in the channel is expressed as: Where V(x, y, z) is the polarized Coulomb field scattering potential, ε0 is the vacuum permittivity, and ε s L is the relative permittivity of the barrier layer. G L is the gate length. GS L is the gate-source distance. GD ρ is the gate-drain spacing, W is the gate width, e is the charge amount, x is the channel along the gate length, y is the channel along the gate width, z is the channel along the longitudinal widening direction, x′ is the position of the additional polarization charge in the x direction, and y′ is the position of the additional polarization charge in the y direction; ρ0 is the polarization charge density in the gate-source region and the gate-drain region; the channel is divided into several grids, each grid corresponding to a coordinate (x1, x2) and a polarization charge density ρ2, ρ1 is the polarization charge density at the leftmost end under the gate, and ρ3 is the polarization charge density at the rightmost end under the gate; From the integration interval and integral terms of formula (3), it can be seen that the scattering intensity of the polarized Coulomb field is related to L GS / L G and L GD / L G The ratio is directly proportional when L GS / L G and L GD / L G As the ratio increases, polarized Coulomb field scattering is enhanced; The method to optimize the transconductance of AlGaN / GaN HFETs is to increase L GS / L G and L GD / L G The ratio enhances polarized Coulomb field scattering, thereby increasing Effectively improve the g of AlGaN / GaN HFET m .

3. The method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization according to claim 2, characterized in that, By reducing the gate length L G This brings the additional polarization charge closer to the electrons under the grating, thereby effectively enhancing the polarization Coulomb field scattering and increasing its intensity. Improving the g of AlGaN / GaN HFET m with f T .

4. The method for improving the transconductance and characteristic frequency of AlGaN / GaN heterojunction field-effect transistors based on device structure optimization according to claim 3, characterized in that, By reducing the gate-source distance L GS This increases the channel electron velocity and improves the g-value of AlGaN / GaN HFETs. m with f T .

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