A method for characterizing field effect mobility of gallium nitride-based double heterojunction HEMT

Abstract

The application discloses a kind of gallium nitride-based double heterojunction HEMT field effect mobility characterization method, including the HEMT to be tested is prepared as the HEMT of fat-FET structure, wherein the HEMT to be tested is gallium nitride-based double heterojunction HEMT, the HEMT of fat-FET structure is the gallium nitride-based double heterojunction HEMT of fat-FET structure.Canal conductance test is carried out to the HEMT of fat-FET structure;The CV characteristic curve of the HEMT of fat-FET structure is tested to obtain first capacitance-voltage variation curve;First capacitance-voltage variation curve is processed by addition;According to preset formula, the field effect mobility-gate voltage curve of upper channel and lower channel is obtained;The electron surface density-gate voltage curve of upper channel and lower channel is obtained respectively;The field effect mobility-electron surface density curve of upper channel and lower channel is obtained respectively.The application can characterize the specific field effect mobility of upper channel and lower channel respectively, improve the characterization accuracy of the field effect mobility of gallium nitride-based double heterojunction HEMT, and be beneficial to the characteristic analysis and process optimization of gallium nitride-based double heterojunction HEMT.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics, specifically relating to a method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs. Background Technology

[0002] Gallium nitride (GaN) materials possess numerous advantages, including a wide bandgap, high electron mobility, high breakdown field strength, high electron saturation velocity, high thermal conductivity, and high quality factor. Furthermore, they can form heterojunction structures and generate a high-concentration two-dimensional electron gas (2DEG) through polarization. Therefore, GaN-based high electron mobility transistors (HEMTs) have promising applications in fields such as space radar, mobile communications, display lighting, and aerospace.

[0003] Gallium nitride (GaN)-based double heterojunction HEMT devices exhibit a natural advantage in strong current-driving capability due to the redistribution of electrons in two channels, resulting in a lower electron surface density in each channel and reduced scattering. Simultaneously, the inherent dual-threshold characteristic of double heterojunction devices allows for improved transconductance flatness through effective modulation, which enhances device linearity. Therefore, GaN-based double heterojunction HEMTs have attracted considerable attention from researchers.

[0004] Traditional methods for measuring the field-effect mobility of devices are derived through transconductance testing. This is applicable when the field-effect transistor operates in the linear region (drain bias voltage V). d Very small (approximately 0.1V), channel carrier mobility μ FE With channel conductance G ch The formula relationship between them is satisfied Among them, L g With W g These are the gate length and gate width of the device under test, respectively, where C is the gate capacitance and V is the gate width. d This is the drain bias voltage. The channel conductance G is obtained by measuring the linear region transfer characteristic curve of the device under test. ch The gate capacitance is obtained by measuring the capacitance voltage (CV), and then the overall field-effect mobility of the gallium nitride-based double heterojunction HEMT under test is obtained.

[0005] However, in the CV test of double heterojunction field-effect transistor (HEMT) devices, as the gate voltage gradually increases, the lower and upper channels of the double heterojunction device turn on sequentially. The corresponding CV characteristic curve shows two rising steps. The first step corresponds to the lower channel turning on, while the second step is related to both the upper and lower channels turning on. Therefore, the capacitance corresponding to the second step is not only related to the upper channel. Traditional field-effect mobility measurement methods directly incorporate capacitance without distinguishing between the two channels. That is, traditional field-effect mobility measurement methods can only characterize the overall field-effect mobility of the device and cannot accurately extract the field-effect mobility of double heterojunction HEMT devices. They cannot characterize the field-effect mobility of the two-dimensional electron gas in the two channels of the double heterojunction device separately, and thus cannot analyze the specific field-effect mobility of the upper and lower channels, affecting the characteristic analysis and process optimization of double heterojunction devices. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs, comprising:

[0007] The HEMT to be tested is fabricated as a fat-FET structure HEMT, wherein the HEMT to be tested is a gallium nitride-based double heterojunction HEMT, and the fat-FET structure HEMT is a gallium nitride-based double heterojunction HEMT with a fat-FET structure.

[0008] Channel conductivity testing was performed when the HEMT with the fat-FET structure was operating in the linear region.

[0009] The CV characteristic curve of the HEMT with the fat-FET structure was tested to obtain the first capacitance-voltage change curve;

[0010] The first capacitor-voltage change curve is summed.

[0011] The field-effect mobility-gate voltage curves of the upper channel and the lower channel are obtained according to the preset formula. The upper channel is the two-dimensional electron gas generated by the heterojunction near the top of the device in the double heterojunction of the fat-FET HEMT, and the lower channel is the two-dimensional electron gas generated by the heterojunction far from the top of the device in the double heterojunction of the fat-FET HEMT.

[0012] Electron surface density-gate voltage curves were obtained for the upper channel and the lower channel, respectively.

[0013] Field-effect mobility-electron surface density curves were obtained for the upper channel and the lower channel, respectively.

[0014] In one embodiment of the present invention, the step of fabricating the HEMT to be tested as a fat-FET structure HEMT includes:

[0015] The fat-FET structure HEMT is prepared based on the HEMT to be tested. The fat-FET structure HEMT is identical to the HEMT to be tested except for the gate length. Furthermore, the gate length of the fat-FET structure HEMT is greater than that of the HEMT to be tested.

[0016] In one embodiment of the present invention, when the HEMT with the fat-FET structure is operating in the linear region, a channel conductance test is performed, including:

[0017] A preset drain bias voltage is added to the drain of the fat-FET HEMT and the source is grounded, so that the fat-FET HEMT operates in the linear region.

[0018] The transfer characteristic curve of the fat-FET structure HEMT is obtained by performing transfer characteristic curve testing. The transconductance characteristic curve of the fat-FET structure HEMT is obtained by differentiating the gate voltage of the transfer characteristic curve with respect to the gate voltage. The horizontal axis of the transconductance characteristic curve is the gate voltage, and the vertical axis of the transconductance characteristic curve is the transconductance of the gallium nitride-based double heterojunction HEMT of the fat-FET structure.

[0019] In one embodiment of the present invention, the first capacitor-voltage change curve is the CV characteristic curve of the HEMT with the fat-FET structure.

[0020] In one embodiment of the present invention, the CV characteristic curve of the fat-FET structure HEMT is tested to obtain a first capacitance-voltage change curve, including:

[0021] The drain of the HEMT with the fat-FET structure is left floating.

[0022] A CV test is performed on the gate and source of the HEMT with the fat-FET structure to obtain the first capacitance-voltage change curve, wherein the horizontal axis of the first capacitance-voltage change curve is the gate voltage of the HEMT with the fat-FET structure, and the vertical axis of the first capacitance-voltage change curve is the capacitance of the HEMT with the fat-FET structure.

[0023] In one embodiment of the present invention, the summation of the first capacitor-voltage change curve includes:

[0024] Obtain the first capacitance corresponding to the gate voltage immediately before the rise of the second step in the first capacitance-voltage change curve, wherein the first step is the step curve corresponding to the negative gate voltage in the double-step phenomenon of the first capacitance-voltage change curve, the first step is the capacitance-voltage curve of the lower channel, and the second step is the step curve corresponding to the positive gate voltage in the double-step phenomenon.

[0025] Obtain the second capacitor and its corresponding gate voltage from the second step curve. Subtract the first capacitor from the second capacitor to obtain the third capacitor.

[0026] A second capacitor-voltage variation curve is obtained based on the gate voltages corresponding to the plurality of third capacitors and the plurality of second capacitors. The second capacitor-voltage variation curve is the CV characteristic curve of the upper channel. The horizontal axis of the second capacitor-voltage variation curve is the gate voltage corresponding to the second capacitor, and the vertical axis of the second capacitor-voltage variation curve is the third capacitor. The third capacitor corresponds to the gate voltage corresponding to the corresponding second capacitor.

[0027] In one embodiment of the present invention, the field-effect mobility-gate voltage curves of the upper channel and the lower channel are obtained according to a preset formula, including:

[0028] Based on the transconductance characteristic curve, the first step of the first capacitance-voltage change curve, and the formula Calculate the field-effect mobility of the lower channel, where μ FE1 L is the field-effect mobility of the lower channel at the first gate voltage. g With W g V represents the gate length and gate width of the HEMT with the fat-FET structure, respectively. d G is the preset drain bias voltage. ch1 C1 is the transconductance corresponding to the first gate voltage in the transconductance characteristic curve, C2 is the capacitance corresponding to the first gate voltage in the first capacitance-voltage change curve, and the first gate voltage is the gate voltage of the first step in the first capacitance-voltage change curve.

[0029] The field-effect mobility-gate voltage curve of the lower channel is obtained based on the field-effect mobility of the lower channel under multiple first gate voltages and multiple first gate voltages.

[0030] Based on the transconductance characteristic curve, the second capacitance-voltage change curve, and the formula Calculate the field-effect mobility of the upper channel, where μ FE2 G represents the field-effect mobility of the upper channel at the second gate voltage. ch2C1 is the transconductance corresponding to the second gate voltage in the transconductance characteristic curve, C2 is the capacitance corresponding to the second gate voltage in the second capacitance-voltage change curve, and the second gate voltage is the gate voltage of the second step in the first capacitance-voltage change curve;

[0031] The field-effect mobility-gate voltage curve of the upper channel is obtained based on the field-effect mobility of the upper channel under multiple second gate voltages and the second gate voltage.

[0032] In one embodiment of the present invention, electron areal density-gate voltage curves of the upper channel and the lower channel are obtained, including:

[0033] Obtain the gate area of ​​the HEMT with the fat-FET structure, divide the value of the ordinate in the first step of the first capacitance-voltage change curve by the gate area to obtain the unit gate capacitance of the lower channel, integrate the unit gate capacitance of the lower channel with the first gate voltage, and then divide it by the unit charge to obtain the electron surface density of the lower channel, and obtain the electron surface density-gate voltage curve of the lower channel based on the first gate voltage and the electron surface density of the lower channel.

[0034] Divide the value of the vertical axis in the second capacitance-voltage change curve by the gate area to obtain the unit gate capacitance of the upper channel. Integrate the unit gate capacitance of the upper channel with respect to the second gate voltage, and then divide it by the unit charge to obtain the electron surface density of the upper channel. Based on the second gate voltage and the electron surface density of the upper channel, obtain the electron surface density-gate voltage curve of the upper channel.

[0035] In one embodiment of the present invention, the field-effect mobility-electron surface density curves of the upper channel and the lower channel are obtained, including:

[0036] The field-effect mobility-gate voltage curve of the lower channel is obtained from the field-effect mobility-gate voltage curve of the lower channel and the electron surface density-gate voltage curve of the lower channel.

[0037] The field-effect mobility-gate voltage curve of the upper channel is obtained from the field-effect mobility-gate voltage curve of the upper channel and the electron surface density-gate voltage curve of the upper channel.

[0038] The present invention has the following beneficial technical effects:

[0039] The field-effect mobility characterization method provided by this invention improves the accuracy of characterizing transconductance as channel conductance by fabricating the device under test as a fat-FET structure, thus improving the accuracy of field-effect mobility characterization. Simultaneously, by summing the first capacitance-voltage change curves, the CV characteristic curves and field-effect mobility of the upper and lower channels are obtained separately. Furthermore, the two-dimensional electron gas field-effect mobility of the two channels of the gallium nitride-based double heterojunction HEMT is characterized using the field-effect mobility-electron surface density curves of the lower and upper channels respectively. This allows for the separate characterization of the specific field-effect mobility of the upper and lower channels, improving the accuracy of field-effect mobility characterization for gallium nitride-based double heterojunction HEMTs and benefiting the characteristic analysis and process optimization of gallium nitride-based double heterojunction HEMTs.

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0041] Figure 1 A schematic flowchart illustrating a method for characterizing the field-effect mobility of a gallium nitride-based double heterojunction HEMT according to an embodiment of the present invention;

[0042] Figures 2a to 2f This is a schematic diagram of the process for fabricating a gallium nitride-based double heterojunction HEMT with a fat-FET structure, provided by an embodiment of the present invention.

[0043] Figure 3 This is a schematic diagram of the transconductance characteristic curve obtained when the HEMT of the fat-FET structure is operating in the linear region, according to the field-effect mobility characterization method provided in the embodiment of the present invention.

[0044] Figure 4 These are the first capacitance-voltage change curve and the second capacitance-voltage change curve obtained in the field-effect mobility characterization method provided in the embodiments of the present invention.

[0045] Figure 5 This is a schematic diagram showing the variation of field-effect mobility of the upper and lower channels of a fat-FET HEMT with gate voltage in the field-effect mobility characterization method provided by the embodiment of the present invention.

[0046] Figure 6 This is a schematic diagram showing the change of electron surface density with gate voltage in a fat-FET structure HEMT using the field-effect mobility characterization method provided in an embodiment of the present invention.

[0047] Figure 7 This is a schematic diagram illustrating the variation of field-effect mobility as a function of electron surface density in a HEMT with a fat-FET structure, based on the field-effect mobility characterization method provided in an embodiment of the present invention. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0049] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified. Furthermore, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or the orientations or positional relationships commonly used when the product is in use. These are used only for the convenience of describing this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this application.

[0050] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0051] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, disclosure, and appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0052] Example 1

[0053] Please see Figure 1 , Figure 1A flowchart illustrating a method for characterizing the field-effect mobility of a gallium nitride-based double heterojunction HEMT according to an embodiment of the present invention is provided. The method includes:

[0054] S10. The HEMT to be tested is fabricated as a fat-FET structure HEMT;

[0055] Specifically, the HEMT to be tested is a gallium nitride-based double heterojunction HEMT, and the fat-FET structure HEMT is a gallium nitride-based double heterojunction HEMT with a fat-FET structure. A fat-FET structure HEMT is fabricated based on the HEMT to be tested, such that the structure of the fat-FET structure HEMT is identical to that of the HEMT to be tested except for the gate length, and the gate length of the fat-FET structure HEMT is greater than that of the HEMT to be tested.

[0056] Furthermore, the gate length of this fat-FET structure HEMT is more than half the distance between the source and drain.

[0057] Please see Figures 2a to 2f , Figures 2a to 2f This invention provides a schematic flowchart for fabricating a gallium nitride-based double heterojunction HEMT with a fat-FET structure. In this embodiment, fabricating the HEMT to be tested as a fat-FET structure specifically includes:

[0058] S101. A double heterojunction material is grown on a silicon nitride substrate using a metal-organic chemical vapor deposition (MOCVD) device.

[0059] like Figure 2a As shown, from bottom to top, the layers are: SiC substrate layer, GaN buffer layer, i-GaN lower channel layer, first AlN insertion layer, InAlN lower barrier layer, i-GaN upper channel layer, second AlN insertion layer, InAlN upper barrier layer, and GaN cap layer.

[0060] Specifically, the SiC substrate layer has a thickness of 350 μm, the i-GaN lower channel layer has a thickness of 300 nm, where i-GaN refers to unintentionally doped gallium nitride, the first AlN insertion layer has a thickness of 1 nm, and the InAlN lower barrier layer is made of In... 0.17 The AlN layer has a thickness of 8 nm, the i-GaN channel layer has a thickness of 10 nm, the second AlN insertion layer has a thickness of 1 nm, and the barrier layer on the InAlN layer is made of In. 0.17 The AlN layer has a thickness of 8 nm, and the GaN cap layer has a thickness of 2 nm.

[0061] S102, Deposit metal in the GaN cap layer to form the source and drain electrodes;

[0062] like Figure 2b As shown, after photolithography on the GaN cap layer, a stacked metal is deposited on the GaN cap layer using an electron beam evaporation device, so that the stacked metal is deposited at the preset source and drain positions. In this embodiment, the preset source and drain positions are specifically on both sides of the GaN cap layer. At the preset source and drain positions, ohmic stacked metal of Ti, Al, Ni, and Au is deposited sequentially from bottom to top, wherein the thickness of Ti is 20nm, the thickness of Al is 160nm, the thickness of Ni is 55nm, and the thickness of Au is 45nm. The entire device is rapidly thermally annealed at 810°C for 50s in an N2 atmosphere, so that the ohmic stacked metal on both sides of the GaN cap layer penetrates down to the upper surface of the i-GaN lower channel layer, forming the source and drain.

[0063] S103. A passivation layer is grown on the GaN cap layer;

[0064] First, ion implantation is used to isolate different HEMT devices. Then, plasma-enhanced chemical vapor deposition (PECVD) is used to deposit a passivation layer on the entire upper surface of the device, such as... Figure 2c As shown, the passivation layer is made of SiN and has a thickness of 120 nm.

[0065] S104. Remove the passivation layer on the source and drain electrodes;

[0066] A dry etching method was used to perform aperture etching above the source and drain electrodes using an inductively coupled plasma (ICP) etching apparatus. Specifically, the chamber pressure of the etching apparatus was set to 5 mTorr, the upper electrode power to be 80 W, and the lower electrode power to be 10 W. Etching was performed using 25 sccm of CF4 and 5 sccm of O2 etching gas within the chamber. Figure 2d As shown, the passivation layer above the source and drain electrodes is etched away.

[0067] S105. Etch the passivation layer located between the source and drain to form the first groove 100.

[0068] like Figure 2e As shown, SiN in the preset gate region is etched using an ICP etching apparatus with F-based etching. The chamber pressure of the etching apparatus is set to 5 mTorr, the upper electrode power of the ICP apparatus is 80 W, and the lower electrode power is 10 W. The first groove 100 is formed by etching in the preset gate region using 25 sccm of etching gas CF4 and 5 sccm of O2 in the chamber.

[0069] S106. Deposit gate metal in the first groove 100 to form a gate.

[0070] like Figure 2f As shown, after photolithography is performed on the entire device, Ni and Au are sequentially deposited on top of the entire device using an electron beam evaporation apparatus, so that the gate metal is deposited into the first groove 100 to form the gate. The thickness of Ni is [missing information]. The thickness of Au is

[0071] The above is the method for fabricating a HEMT with a fat-FET structure provided in this embodiment. This invention does not limit the method for fabricating a HEMT with a fat-FET structure.

[0072] The field-effect mobility of gallium nitride-based double heterojunction HEMT devices is positively correlated with the channel conductance. The channel conductance is usually characterized by the transconductance value of the gallium nitride-based double heterojunction HEMT device. Compared with the HEMT device under test, the fat-FET structure HEMT is the same as the HEMT device under test except for the gate length. Therefore, the field-effect mobility of the fat-FET structure HEMT can characterize the field-effect mobility of the HEMT under test. Furthermore, since the gate length of the fat-FET structure HEMT is relatively long, the spacing between the gate and the source and the spacing between the gate and the drain are relatively small compared with the gate length. Therefore, the fat-FET structure HEMT can reduce the influence of the gate-source series resistance and the gate-drain series resistance, making the transconductance value closer to the channel conductance, thereby improving the accuracy of the field-effect mobility characterization of the fat-FET structure HEMT.

[0073] S20. Channel conductivity test is performed when the HEMT with fat-FET structure is operating in the linear region.

[0074] Specifically, a preset drain bias voltage is added to the drain of the HEMT with the fat-FET structure, and the source is grounded, so that the HEMT with the fat-FET structure operates in the linear region;

[0075] The transfer characteristic curve of the HEMT with the fat-FET structure was obtained by testing the linear region using a DC test device. The transconductance characteristic curve of the HEMT with the fat-FET structure was obtained by differentiating the transfer characteristic curve with respect to the gate voltage. The horizontal axis of the transconductance characteristic curve is the gate voltage of the HEMT with the fat-FET structure, and the vertical axis of the transconductance characteristic curve is the transconductance of the HEMT with the fat-FET structure.

[0076] Please see Figure 3 , Figure 3 This is a schematic diagram of the transconductance characteristic curve obtained when a fat-FET HEMT operates in the linear region, according to the field-effect mobility characterization method provided in this embodiment of the invention. In this embodiment, the preset drain bias voltage is 0.1V, at which point the fat-FET HEMT is in the linear operating region. The gate voltage is set to scan from -11V to 3V with a step size of 0.1V, and the source is grounded to obtain the transfer characteristic curve and the transconductance characteristic curve. In this schematic diagram of the transconductance characteristic curve, the horizontal axis represents the gate voltage (V) of the fat-FET HEMT, which ranges from Vg0 (approximately -11V) to Vg2 (3V); the vertical axis represents the transconductance value (S) of the fat-FET HEMT, that is, the transconductance value corresponding to the gate voltage Vg0 to Vg2.

[0077] S30. The first capacitance-voltage change curve is obtained by performing CV characteristic curve testing on a gallium nitride-based double heterojunction HEMT with a fat-FET structure.

[0078] First, the drain of the HEMT with the fat-FET structure is left floating;

[0079] Subsequently, a cross-sectional area (CV) test was performed on the gate and source of the HEMT with the fat-FET structure. The gate voltage was scanned from -11V to 3V in 0.1V steps, and the source was grounded, resulting in a first capacitance-voltage variation curve. Specifically, this first capacitance-voltage variation curve is the CV characteristic curve of the HEMT with the fat-FET structure. The horizontal axis of the first capacitance-voltage variation curve represents the gate voltage of the HEMT with the fat-FET structure, and the vertical axis represents the capacitance of the HEMT with the fat-FET structure. The horizontal axis of the first capacitance-voltage variation curve has the same range as the horizontal axis of the transconductance characteristic curve, that is, the gate voltage of the first capacitance-voltage variation curve is taken as the gate voltage of the transconductance characteristic curve. In other embodiments, the first capacitance-voltage variation curve can also be obtained using a ring diode structure.

[0080] S40. Sum the first capacitor-voltage change curve;

[0081] The first capacitance-voltage change curve typically exhibits a double-step phenomenon. The first step in this double-step phenomenon is the step curve corresponding to a negative gate voltage. The first step is the capacitance-voltage curve of the lower channel, and the second step is the step curve corresponding to a positive gate voltage. The upper channel is the two-dimensional electron gas generated by the heterojunction near the top of the device in the double heterojunction of the fat-FET HEMT structure, and the lower channel is the two-dimensional electron gas generated by the heterojunction away from the top of the device in the double heterojunction of the fat-FET HEMT structure. In this embodiment, the upper channel is the two-dimensional electron gas generated by the heterojunction formed by the i-GaN upper channel layer and the InAlN upper barrier layer, and the lower channel is the two-dimensional electron gas generated by the heterojunction formed by the i-GaN lower channel layer and the InAlN lower barrier layer.

[0082] The summation process for the first capacitor-voltage change curves specifically includes:

[0083] Obtain the first capacitor corresponding to the gate voltage immediately before the rise of the second step in the first capacitor-voltage change curve, wherein the gate voltage immediately before the rise of the second step is the gate voltage corresponding to the upper channel being about to turn on but not yet turned on; obtain the second capacitor in the second step curve and the gate voltage corresponding to the second capacitor, and subtract the first capacitor from the second capacitor to obtain the third capacitor;

[0084] The second capacitor-voltage variation curve is obtained based on the gate voltages corresponding to multiple third capacitors and multiple second capacitors. The horizontal axis of the second capacitor-voltage variation curve is the gate voltage corresponding to the second capacitor. The value of this horizontal axis is the same as the horizontal axis value of the second step in the first capacitor-voltage variation curve. The vertical axis of the second capacitor-voltage variation curve is the third capacitor. The third capacitor corresponds to the gate voltage corresponding to the corresponding second capacitor. The second capacitor-voltage variation curve is the CV characteristic curve of the upper channel.

[0085] Please see Figure 4 , Figure 4These are first and second capacitance-voltage variation curves obtained using the field-effect mobility characterization method provided in this embodiment of the invention. The horizontal axis represents the gate voltage (V), and the vertical axis represents the capacitance (F). In this embodiment, in the first capacitance-voltage variation curve, when the gate voltage is greater than Vg1 (approximately 0.2V), the lower channel electrons are saturated. That is, the capacitance corresponding to the gate voltages Vg0 to Vg1 represents the CV characteristic curve of the lower channel. In the second capacitance-voltage variation curve, the capacitance corresponding to the gate voltages Vg1 to Vg2 represents the CV characteristic curve of the upper channel. Specifically, within the gate voltage range of Vg1 to Vg2, the capacitance value of the second capacitance-voltage variation curve under the same gate voltage is obtained by subtracting the capacitance value corresponding to 0.2V from the capacitance value of the first capacitance-voltage variation curve.

[0086] The field-effect mobility characterization method provided in this embodiment, in the first capacitance-voltage variation curve, when the gate voltage is greater than the gate voltage corresponding to the first capacitor, the lower channel electron concentration of the HEMT with the fat-FET structure is saturated. At this time, the CV characteristic curve of the lower channel is saturated, and the first capacitor is the saturation capacitance value of the lower channel. The second step in the first capacitance-voltage variation curve is caused by the combined effect of the increase in upper channel electron concentration and the saturation of lower channel electron concentration. Therefore, the second step of the first capacitance-voltage variation curve is the sum of the CV characteristic curves of the upper and lower channels. Keeping the gate voltage value of the second step constant, the CV characteristic curve of the upper channel can be obtained by subtracting the saturation capacitance value of the lower channel from the capacitance value of the second step. This embodiment obtains different CV characteristic curves for the upper and lower channels by summing the first capacitance-voltage variation curves, which can more accurately characterize the capacitance-voltage variation of the HEMT with the fat-FET structure.

[0087] S50. Obtain the field-effect mobility-gate voltage curves for the upper and lower channels respectively according to the preset formula;

[0088] The field-effect mobility-gate voltage curve of the lower channel, obtained according to the preset formula, specifically includes:

[0089] S501, based on the transconductance characteristic curve, the first step of the first capacitor-voltage change curve, and the formula... The field-effect mobility of the lower channel is obtained;

[0090] Specifically, μ FE1 L is the field-effect mobility of the lower channel at the first gate voltage. g With W g These represent the gate length and gate width of a fat-FET structure HEMT, respectively. d G is the preset drain bias voltage for channel conduction testing of a fat-FET structure HEMT. ch1C1 is the transconductance corresponding to the first gate voltage in the transconductance characteristic curve, and C2 is the capacitance corresponding to the first gate voltage in the first capacitance-voltage change curve. The first gate voltage is the gate voltage corresponding to the first step in the first capacitance-voltage change curve. In this embodiment, the range of the first gate voltage is from Vg0 to Vg1.

[0091] S502. Based on the field-effect mobility of the lower channel under multiple first gate voltages and the multiple first gate voltages, obtain the field-effect mobility-gate voltage curve of the lower channel.

[0092] Specifically, the horizontal axis of the field-effect mobility-gate voltage curve of the lower channel is the first gate voltage, and the vertical axis of the field-effect mobility-gate voltage curve of the lower channel is the field-effect mobility of the lower channel under the first gate voltage.

[0093] The field-effect mobility-gate voltage curve of the upper channel, obtained according to the preset formula, specifically includes:

[0094] S503, based on the transconductance characteristic curve, the second capacitor-voltage change curve, and the formula. Calculate the field-effect mobility of the upper channel;

[0095] Specifically, μ FE2 Gch2 is the field-effect mobility of the upper channel under the second gate voltage, Gch2 is the transconductance corresponding to the second gate voltage in the transconductance characteristic curve, and C2 is the capacitance corresponding to the second gate voltage in the second capacitance-voltage change curve. The second gate voltage is the gate voltage corresponding to the second step in the first capacitance-voltage change curve. In this embodiment, the range of the second gate voltage is from Vg1 to Vg2.

[0096] S504. Based on the field-effect mobility of the upper channel under multiple second gate voltages and the second gate voltage, obtain the field-effect mobility-gate voltage curve of the upper channel.

[0097] Specifically, the horizontal axis of the upper channel field-effect mobility-gate voltage curve represents the second gate voltage, and the vertical axis of the upper channel field-effect mobility-gate voltage curve represents the upper channel field-effect mobility at the second gate voltage.

[0098] Please see Figure 5 , Figure 5 This is a schematic diagram illustrating the variation of field-effect mobility of the upper and lower channels of a fat-FET HEMT structure with gate voltage in the field-effect mobility characterization method provided by an embodiment of the present invention. The horizontal axis represents the gate voltage (V) and is the same as the horizontal axis in the first capacitor-voltage variation curve. The vertical axis represents the field-effect mobility (cm). 2 / Vs). Among them, the gate voltage from -11V to 0.2V, i.e., Vg0 to Vg1, corresponds to the field-effect mobility of the lower channel, and the gate voltage from 0.2V to 3V, i.e., Vg1 to Vg2, corresponds to the field-effect mobility of the upper channel.

[0099] S60. Obtain the electron surface density-gate voltage curves for the upper and lower channels, respectively.

[0100] S601. Obtain the electron surface density-gate voltage curve of the lower channel;

[0101] The gate area of ​​the HEMT with the fat-FET structure is obtained. The value of the vertical axis in the first step of the first capacitance-voltage change curve is divided by the gate area to obtain the unit gate capacitance value of the lower channel. The unit gate capacitance of the lower channel is integrated with the first gate voltage and then divided by the unit charge to obtain the electron areal density of the lower channel. The electron areal density-gate voltage curve of the lower channel is obtained based on the first gate voltage and the electron areal density of the lower channel. Specifically, the horizontal axis of the electron areal density-gate voltage curve of the lower channel is the first gate voltage and the vertical axis is the electron areal density of the lower channel.

[0102] S602. Obtain the electron surface density-gate voltage curve of the upper channel;

[0103] Divide the value of the vertical axis in the second capacitance-voltage change curve by the gate area to obtain the unit gate capacitance value of the upper channel. Integrate the unit gate capacitance of the upper channel with respect to the second gate voltage, and then divide it by the unit charge to obtain the electron surface density of the upper channel. Based on the second gate voltage and the electron surface density of the upper channel, obtain the electron surface density-gate voltage curve of the upper channel. Specifically, the horizontal axis of the electron surface density-gate voltage curve of the upper channel is the second gate voltage, and the vertical axis is the electron surface density of the upper channel.

[0104] Please see Figure 6 , Figure 6 This is a schematic diagram illustrating the electron surface density of a fat-FET structure HEMT as a function of gate voltage in the field-effect mobility characterization method provided by an embodiment of the present invention. The horizontal axis represents the gate voltage (V), and the vertical axis represents the electron surface density (cm²). -2 ), where the gate voltage from -11V to 0.2V, i.e. Vg0 to Vg1, corresponds to the electron surface density of the lower channel, and the gate voltage from 0.2V to 3V, i.e. Vg1 to Vg2, corresponds to the electron surface density of the upper channel.

[0105] S70. Field-effect mobility-electron surface density curves for the upper and lower channels were obtained, respectively.

[0106] S701. Obtain the field-effect mobility-gate voltage curve of the lower channel based on the field-effect mobility-gate voltage curve and the electron surface density-gate voltage curve of the lower channel.

[0107] Specifically, obtain the field-effect mobility of the lower channel corresponding to the third gate voltage in the field-effect mobility-gate voltage curve, and obtain the electron surface density value of the lower channel corresponding to the third gate voltage in the electron surface density-gate voltage curve. Repeat the above operations to obtain multiple field-effect mobility values ​​and electron surface density values ​​of the lower channel corresponding to the third gate voltage. Plot the field-effect mobility-electron surface density curve of the lower channel with the electron surface density value of the lower channel as the abscissa and the field-effect mobility of the lower channel as the ordinate.

[0108] S702. Based on the field-effect mobility-gate voltage curve and the electron surface density-gate voltage curve of the upper channel, the field-effect mobility-electron surface density curve of the upper channel is obtained.

[0109] Specifically, obtain the field-effect mobility of the upper channel corresponding to the fourth gate voltage in the field-effect mobility-gate voltage curve, and obtain the electron surface density value of the upper channel corresponding to the fourth gate voltage in the electron surface density-gate voltage curve. Repeat the above operations to obtain multiple field-effect mobility values ​​and electron surface density values ​​of the upper channel corresponding to multiple fourth gate voltages. Plot the field-effect mobility-electron surface density curve of the upper channel with the electron surface density value of the upper channel as the abscissa and the field-effect mobility of the upper channel as the ordinate.

[0110] Please see Figure 7 , Figure 7 This is a schematic diagram illustrating the variation of the field-effect mobility of a fat-FET structure HEMT with electron surface density in the field-effect mobility characterization method provided by the embodiments of the present invention. The horizontal axis represents the electron surface density (cm²). -2 The vertical axis represents the field-effect mobility (cm). 2 As can be seen from / Vs), the field-effect mobility-electron surface density of the lower channel is significantly higher than that of the upper channel.

[0111] The field-effect mobility characterization method provided in this embodiment improves the accuracy of characterizing transconductance as channel conductance by fabricating the device under test as a fat-FET structure, thus improving the accuracy of field-effect mobility characterization. Simultaneously, the first capacitance-voltage change curve is summed to obtain the CV characteristic curves of the upper and lower channels, respectively. Furthermore, the two-dimensional electron gas field-effect mobility of the two channels of the gallium nitride-based double heterojunction HEMT is characterized using the field-effect mobility-electron surface density curves of the lower and upper channels, respectively. This further improves the characterization accuracy of the field-effect mobility of the gallium nitride-based double heterojunction HEMT, which is beneficial for the characteristic analysis and process optimization of gallium nitride-based double heterojunction HEMTs.

[0112] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs, characterized in that, include: The HEMT to be tested is fabricated as a fat-FET structure HEMT, wherein the HEMT to be tested is a gallium nitride-based double heterojunction HEMT, and the fat-FET structure HEMT is a gallium nitride-based double heterojunction HEMT with a fat-FET structure. Channel conductivity testing was performed when the HEMT with the fat-FET structure was operating in the linear region. The CV characteristic curve of the HEMT with the fat-FET structure was tested to obtain the first capacitance-voltage change curve; The first capacitor-voltage change curve is summed. The field-effect mobility-gate voltage curves of the upper channel and the lower channel are obtained according to the preset formula. The upper channel is the two-dimensional electron gas generated by the heterojunction near the top of the device in the double heterojunction of the fat-FET HEMT, and the lower channel is the two-dimensional electron gas generated by the heterojunction far from the top of the device in the double heterojunction of the fat-FET HEMT. Electron surface density-gate voltage curves were obtained for the upper channel and the lower channel, respectively. Field-effect mobility-electron surface density curves were obtained for the upper channel and the lower channel, respectively.

2. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 1, characterized in that, The process of fabricating the HEMT to be tested as a fat-FET structure includes: The fat-FET structure HEMT is prepared based on the HEMT to be tested. The fat-FET structure HEMT is identical to the HEMT to be tested except for the gate length. Furthermore, the gate length of the fat-FET structure HEMT is greater than that of the HEMT to be tested.

3. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 2, characterized in that, When the HEMT with the fat-FET structure is operating in the linear region, channel conductivity testing is performed, including: A preset drain bias voltage is added to the drain of the fat-FET HEMT and the source is grounded, so that the fat-FET HEMT operates in the linear region. The transfer characteristic curve of the fat-FET structure HEMT is obtained by performing transfer characteristic curve testing. The transconductance characteristic curve of the fat-FET structure HEMT is obtained by differentiating the gate voltage of the transfer characteristic curve with respect to the gate voltage. The horizontal axis of the transconductance characteristic curve is the gate voltage, and the vertical axis of the transconductance characteristic curve is the transconductance of the gallium nitride-based double heterojunction HEMT of the fat-FET structure.

4. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 3, characterized in that, The first capacitor-voltage change curve is the CV characteristic curve of the HEMT with the fat-FET structure.

5. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 4, characterized in that, The CV characteristic curve of the HEMT with the fat-FET structure was tested to obtain the first capacitance-voltage change curve, including: The drain of the HEMT with the fat-FET structure is left floating. A CV test is performed on the gate and source of the HEMT with the fat-FET structure to obtain the first capacitance-voltage change curve, wherein the horizontal axis of the first capacitance-voltage change curve is the gate voltage of the HEMT with the fat-FET structure, and the vertical axis of the first capacitance-voltage change curve is the capacitance of the HEMT with the fat-FET structure.

6. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 5, characterized in that, The first capacitor-voltage change curve is summed, including: Obtain the first capacitance corresponding to the gate voltage immediately before the rise of the second step in the first capacitance-voltage change curve, wherein the first step is the step curve corresponding to the negative gate voltage in the double-step phenomenon of the first capacitance-voltage change curve, the first step is the capacitance-voltage curve of the lower channel, and the second step is the step curve corresponding to the positive gate voltage in the double-step phenomenon. Obtain the second capacitor and its corresponding gate voltage from the second step curve. Subtract the first capacitor from the second capacitor to obtain the third capacitor. A second capacitor-voltage variation curve is obtained based on the gate voltages corresponding to the plurality of third capacitors and the plurality of second capacitors. The second capacitor-voltage variation curve is the CV characteristic curve of the upper channel. The horizontal axis of the second capacitor-voltage variation curve is the gate voltage corresponding to the second capacitor, and the vertical axis of the second capacitor-voltage variation curve is the third capacitor. The third capacitor corresponds to the gate voltage corresponding to the corresponding second capacitor.

7. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 6, characterized in that, The field-effect mobility-gate voltage curves for the upper and lower channels are obtained according to the preset formula, including: Based on the transconductance characteristic curve, the first step of the first capacitance-voltage change curve, and the formula Calculate the field-effect mobility of the lower channel, where μ FE1 L is the field-effect mobility of the lower channel at the first gate voltage. g With W g V represents the gate length and gate width of the HEMT with the fat-FET structure, respectively. d G is the preset drain bias voltage. ch1 C1 is the transconductance corresponding to the first gate voltage in the transconductance characteristic curve, C2 is the capacitance corresponding to the first gate voltage in the first capacitance-voltage change curve, and the first gate voltage is the gate voltage of the first step in the first capacitance-voltage change curve. The field-effect mobility-gate voltage curve of the lower channel is obtained based on the field-effect mobility of the lower channel under multiple first gate voltages and multiple first gate voltages. Based on the transconductance characteristic curve, the second capacitance-voltage change curve, and the formula Calculate the field-effect mobility of the upper channel, where μ FE2 G represents the field-effect mobility of the upper channel at the second gate voltage. ch2 C1 is the transconductance corresponding to the second gate voltage in the transconductance characteristic curve, C2 is the capacitance corresponding to the second gate voltage in the second capacitance-voltage change curve, and the second gate voltage is the gate voltage of the second step in the first capacitance-voltage change curve; The field-effect mobility-gate voltage curve of the upper channel is obtained based on the field-effect mobility of the upper channel under multiple second gate voltages and the second gate voltage.

8. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 7, characterized in that, The electron areal density-gate voltage curves for the upper channel and the lower channel are obtained respectively, including: Obtain the gate area of ​​the HEMT with the fat-FET structure, divide the value of the ordinate in the first step of the first capacitance-voltage change curve by the gate area to obtain the unit gate capacitance of the lower channel, integrate the unit gate capacitance of the lower channel with the first gate voltage, and then divide it by the unit charge to obtain the electron surface density of the lower channel, and obtain the electron surface density-gate voltage curve of the lower channel based on the first gate voltage and the electron surface density of the lower channel. Divide the value of the vertical axis in the second capacitance-voltage change curve by the gate area to obtain the unit gate capacitance of the upper channel. Integrate the unit gate capacitance of the upper channel with respect to the second gate voltage, and then divide it by the unit charge to obtain the electron surface density of the upper channel. Based on the second gate voltage and the electron surface density of the upper channel, obtain the electron surface density-gate voltage curve of the upper channel.

9. The method for characterizing the field-effect mobility of gallium nitride-based double heterojunction HEMTs according to claim 8, characterized in that, The field-effect mobility-electron surface density curves of the upper channel and the lower channel were obtained, respectively, including: The field-effect mobility-gate voltage curve of the lower channel is obtained from the field-effect mobility-gate voltage curve of the lower channel and the electron surface density-gate voltage curve of the lower channel. The field-effect mobility-gate voltage curve of the upper channel is obtained from the field-effect mobility-gate voltage curve of the upper channel and the electron surface density-gate voltage curve of the upper channel.

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