Dynamic thermal characteristic characterization method for GaN HEMT radio frequency device

Abstract

The invention relates to a dynamic thermal characteristic characterization method for a GaN HEMT (High Electron Mobility Transistor) radio frequency device. The method comprises the following steps: acquiring structural parameters of the GaN HEMT radio frequency device Establishing a three-dimensional finite element thermal model according to the structure parameters of the GaN HEMT radio frequency device; adjusting material parameters of the three-dimensional finite element thermal model according to an infrared thermal imaging test result of the GaN HEMT radio frequency device; based on the three-dimensional finite element thermal model, simulation is carried out under different environment temperatures and dissipation powers, thermal resistance of the GaN HEMT radio frequency device is obtained, and the relation between the thermal resistance and the environment temperatures and the dissipation powers is obtained; and establishing a Foster-form third-order RC heater network model of the GaN HEMT radio frequency device on the basis of the relationship between the thermal resistance and the ambient temperature as well as between the thermal resistance and the dissipated power and in combination with the transient pulse current response of the GaN HEMT radio frequency device. According to the invention, the transient thermal characteristics of the device under different working conditions can be rapidly represented.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor devices, and in particular to a method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device. Background Art

[0002] Gallium nitride high electron mobility transistor (GaN HEMT) devices are widely used in RF microwave fields such as power amplifiers, low noise amplifiers, filters and switches due to their excellent performance. Compared with Si and GaAs devices, GaN has a larger bandgap width and therefore a higher breakdown voltage. Due to the polarization effect, GaN HEMT conducts electricity through a very thin layer of two-dimensional electron gas formed at the AlGaN / GaN heterojunction, which makes it have higher electron mobility and electron saturation velocity. It is one of the most advantageous semiconductor RF devices to date. However, since GaN HEMT devices usually have higher power density and operate in high-frequency and high-power scenarios, a large amount of self-heating inside them will cause the temperature to rise and the device performance to change. Thermal resistance is usually used to reflect the severity of the device's self-heating effect. The calculation formula is: Where ΔT is the device temperature rise, P diss To dissipate power in the device, accurate steady-state thermal resistance extraction plays an important role in the thermal management of GaN HEMT RF devices and the prediction of the mean time to failure of the device. Currently, the steady-state thermal resistance extraction method has been widely studied, but GaN HEMT RF devices actually work under RF and pulse signals. Therefore, it is necessary to quantify the dynamic thermal characteristics of GaN HEMT RF devices.

[0003] When a GaN HEMT RF device operates under fixed DC bias conditions for a period of time, its internal state is quasi-steady, and the device thermal response is only related to thermal resistance. When the device is in pulse or RF continuous wave conditions, the device thermal response will change over time. The current methods for extracting transient thermal characteristics of devices mainly include temperature-sensitive electrical parameter method, reflectivity thermal imaging method, finite element transient thermal simulation method, and multi-order thermal subnetwork method.

[0004] The temperature-sensitive electrical parameter method can measure the transient thermal response of the device by measuring the electrical parameters of the GaN HEMT RF device, such as the on-resistance and gate Schottky contact resistance, which vary approximately linearly with temperature. However, this method can only obtain the average temperature in the device channel rather than the peak temperature, so the measured temperature is lower than the actual temperature. The reflectivity thermal imaging method uses the principle that the intensity of reflected light on the surface of the material changes with temperature to measure the temperature distribution on the surface of the device. This method can achieve sub-micron spatial resolution and nanosecond temporal resolution, but the experimental equipment of this method is expensive and the operation is complicated. It ignores the change in the reflectivity of the device surface caused by temperature change, and there is a large measurement error when the device temperature is too high (such as above 200°C). The finite element transient thermal simulation method can obtain the transient thermal response of the device by setting the thermal conductivity, density and constant pressure heat capacity of the device material. However, due to the uncertainty of the process, there are errors in the material parameter setting and it cannot be measured. In addition, the finite element transient thermal simulation is relatively time-consuming and is not suitable for quickly obtaining the transient thermal response of the device. The multi-order thermal subnetwork method is a commonly used method for characterizing the transient thermal response of GaN HEMT RF devices. By extracting the multi-order thermal subnetwork composed of the thermal resistance and thermal capacitance of the device, the transient thermal response of the device can be quickly obtained.

[0005] At present, the commonly used thermal resistance extraction methods are divided into two categories: experimental extraction method and simulation extraction method. Among them, the experimental extraction methods include optical extraction method, electrical extraction method and physical contact method. The electrical extraction method includes methods such as comparing DC test and pulse test under different environments, extracting the junction-shell thermal resistance through the structure function method, etc., but it can only obtain the average temperature in the device channel, and because it ignores the self-heating effect under pulse conditions, it will underestimate the device thermal resistance to a certain extent. The physical contact method can achieve nanometer-level thermal resistance measurement accuracy, but due to the complex operation, expensive equipment and the inability to determine the contact thermal resistance between the physical contact probe and the device, it has a large measurement uncertainty. At present, the most commonly used thermal resistance measurement method is still the optical measurement method. Among them, Raman spectroscopy and thermal reflectivity imaging have high imaging accuracy, but they cannot obtain the temperature distribution in a large range of the device. The infrared thermal imaging method is widely used in the thermal resistance test of GaN HEMT devices because of its advantages such as simple operation and ability to measure the device surface heat distribution in a large range of the device. However, it can only obtain the device surface temperature and has a low spatial resolution, so it needs to be combined with steady-state finite element thermal simulation. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for characterizing the dynamic thermal characteristics of a GaN HEMT radio frequency device, which can quickly characterize the transient thermal characteristics of the device under different working conditions.

[0007] The technical solution adopted by the present invention to solve the technical problem is: to provide a method for characterizing the dynamic thermal characteristics of a GaN HEMT radio frequency device, comprising the following steps:

[0008] S1, obtaining the structural parameters of the GaN HEMT RF device;

[0009] S2, establishing a three-dimensional finite element thermal model according to the structural parameters of the GaN HEMT radio frequency device;

[0010] S3, adjusting the material parameters of the three-dimensional finite element thermal model according to the infrared thermal imaging test results of the GaN HEMT radio frequency device;

[0011] S4, based on the three-dimensional finite element thermal model, simulation is performed under different ambient temperatures and dissipated powers to obtain the thermal resistance of the GaN HEMT radio frequency device, and obtain the relationship between the thermal resistance and the ambient temperature and the dissipated power;

[0012] S5, based on the relationship between thermal resistance, ambient temperature and dissipated power and combined with the transient pulse current response of the GaN HEMT radio frequency device, a third-order RC thermal sub-network model of the GaN HEMT radio frequency device in Foster form is established.

[0013] In the step S1, the structural parameters of the GaN HEMT radio frequency device are obtained by using a transmission electron microscope and an optical microscope.

[0014] The step S2 also includes: setting the thermal conductivity and interface thermal resistance of the material.

[0015] The step S3 specifically includes: performing Gaussian filtering on the surface temperature distribution of the three-dimensional finite element thermal model according to the spatial resolution of infrared thermal imaging, comparing the filtered result with the infrared thermal imaging test result of the GaN HEMT radio frequency device, and adjusting the material parameters of the three-dimensional finite element thermal model until the filtered result fits the infrared thermal imaging test result of the GaN HEMT radio frequency device.

[0016] The relationship between the thermal resistance, the ambient temperature and the dissipated power in step S4 is expressed as: th =aT base +bP diss +c, where R th is the thermal resistance, T base is the ambient temperature, P diss is the dissipated power, and a, b, c are coefficients.

[0017] The step S5 specifically includes:

[0018] According to the change of the isothermal line shape, the GaN HEMT radio frequency device is divided into three regions from top to bottom, wherein each region corresponds to a first-order RC thermal sub-network;

[0019] A third-order RC thermal subnetwork in Foster form is used to describe the transient thermal characteristics of the GaN HEMT RF device;

[0020] Under the condition of fixed bias conditions, the leakage current of the GaN HEMT radio frequency device is approximately linearly related to the channel peak temperature, and the transient current response coefficients of each order obtained by fitting are proportional to the thermal resistance of each order;

[0021] According to the Foster form of the third-order RC thermal subnetwork description and the transient current response coefficient of each order is proportional to the thermal resistance of each order, the thermal resistance and thermal capacity of each order of the third-order RC thermal subnetwork are fitted.

[0022] The third-order RC thermal subnetwork adopting the Foster form satisfies the following relationship: Among them, τ i is the time constant of the ith first-order RC thermal subnetwork, R i is the thermal resistance of the i-th first-order RC thermal subnetwork, T(t) is the dissipated power P diss The peak channel temperature of the GaN HEMT RF device changes as a function of time, T base is the ambient temperature.

[0023] The transient response of the leakage current of the GaN HEMT RF device under pulse excitation is expressed as: Where, I(t) is the leakage current of GaN HEMT RF device, I 0 is the leakage current of the GaN HEMT RF device when it reaches steady state under pulse bias voltage conditions, A i is the i-th order transient current response coefficient, τ i is the time constant of the i-th first-order RC thermal subnetwork.

[0024] The method for characterizing the dynamic thermal characteristics of the GaN HEMT RF device also includes: recalculating the total thermal resistance of the GaN HEMT RF device under different bias conditions, redistributing the total thermal resistance through the relationship that each order of transient current response coefficient is proportional to each order of thermal resistance, calculating the time constant of each order of thermal sub-network, and comparing the transient current response of the GaN HEMT RF device obtained by actual measurement and fitting.

[0025] Beneficial Effects

[0026] Due to the adoption of the above technical scheme, the present invention has the following advantages and positive effects compared with the prior art: the present invention accurately obtains the device structure through a focused ion beam, a transmission electron microscope and an optical microscope; the three-dimensional finite element thermal simulation model of the GaN HEMT device is calibrated through infrared thermal imaging results, and the thermal resistance value of the device related to the dissipated power and the ambient temperature is obtained from the calibrated model; based on the transient pulse current response of the device, a third-order RC thermal sub-network model of the GaN HEMT device in the Foster form is established, which can quickly characterize the transient thermal characteristics of the device under different working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of a method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to an embodiment of the present invention;

[0028] Figure 2 It is a flow chart of three-dimensional finite element thermal simulation verified by infrared thermal imaging in an embodiment of the present invention;

[0029] Figure 3 is a comparison diagram of infrared thermal imaging and thermal simulation results at the central axis of the device in an embodiment of the present invention;

[0030] Figure 4 is a comparison chart of simulation results and measured results under different ambient temperatures and dissipated powers in an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of device thermal resistance values ​​obtained by simulation under different ambient temperatures and dissipated powers in an embodiment of the present invention;

[0032] Figure 6 Schematic diagram of the heat conduction process of a GaN HEMT device in an embodiment of the present invention;

[0033] Figure 7 It is a third-order Foster-form thermal subnetwork topology diagram in an embodiment of the present invention;

[0034] Figure 8 is a transient pulse current fitting result diagram in an embodiment of the present invention;

[0035] Fig. 9 is a transient thermal response diagram obtained by thermal subnetwork fitting in an embodiment of the present invention;

[0036] Fig.10 It is a comparison diagram of transient current responses obtained by actual measurement and fitting under different bias voltages in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0038] The embodiment of the present invention relates to a method for characterizing the dynamic thermal characteristics of a GaN HEMT radio frequency device, such as Figure 1 As shown, the following steps are included:

[0039] Step S1, obtaining the structural parameters of the GaN HEMT radio frequency device. In this step, a transmission electron microscope (TEM) and an optical microscope may be used to obtain the structural parameters of the GaN HEMT radio frequency device.

[0040] Step S2, establishing a three-dimensional finite element thermal model according to the structural parameters of the GaN HEMT radio frequency device; this step also includes setting parameters such as the thermal conductivity and interface thermal resistance of the material.

[0041] Step S3, adjusting the material parameters of the three-dimensional finite element thermal model according to the infrared thermal imaging test results of the GaN HEMT RF device. This step is specifically: Gaussian filtering the surface temperature distribution of the three-dimensional finite element thermal model according to the infrared thermal imaging spatial resolution, and comparing the filtered result with the infrared thermal imaging test result of the GaN HEMT RF device, and adjusting the material parameters of the three-dimensional finite element thermal model until the filtered result fits the infrared thermal imaging test result of the GaN HEMT RF device. The process is as follows Figure 2 The fitting results are shown in Figure 3 To verify the accuracy of the model, this step also requires comparison of simulation and experimental results at different ambient temperatures and dissipated powers. The results are shown in Figure 4 shown.

[0042] Step S4, based on the three-dimensional finite element thermal model, simulation is performed under different ambient temperatures and dissipated powers to obtain the thermal resistance of the GaN HEMT radio frequency device, and obtain the relationship between the thermal resistance and the ambient temperature and the dissipated power; Figure 5 is the simulation result under different working conditions. The relationship between thermal resistance, ambient temperature and dissipated power obtained by the final fitting is:

[0043] R th =0.04533×T base +0.488×P diss +9.912

[0044] Among them, R th is the thermal resistance, Tbase is the ambient temperature, P diss is the dissipated power.

[0045] Step S5, based on the relationship between thermal resistance, ambient temperature and dissipated power and combined with the transient pulse current response of the GaN HEMT radio frequency device, a third-order RC thermal sub-network model of the GaN HEMT radio frequency device in Foster form is established.

[0046] Since there are multiple layers of materials from the device channel area to the bottom of the heat sink, such as Figure 6 As shown, the first-order RC thermal subnetwork cannot be simply used to accurately simulate and describe the transient thermal response of the device. Therefore, in this embodiment, first, according to the change of the isothermal line shape, the GaN HEMT RF device is divided into three regions from top to bottom, namely, the GaN buffer layer plus interface thermal resistance region, the SiC substrate region and the solder layer heat sink region, and these three regions correspond to a first-order RC thermal subnetwork respectively.

[0047] Although the parameters of the Cauer thermal subnetwork correspond to the actual structure layer of the device and have clear physical meanings, their mathematical expressions are very complex and are not conducive to fitting with measured data. Therefore, this embodiment uses a third-order RC thermal subnetwork in the form of Foster to describe the transient thermal characteristics of the GaN HEMT RF device, such as Figure 7 As shown, it satisfies the following relationship:

[0048] τ i =R i C i ,i=1,2,3 (1)

[0049]

[0050]

[0051] Among them, τ i is the time constant of the ith first-order RC thermal subnetwork, R i is the thermal resistance of the i-th first-order RC thermal subnetwork, T(t) is the dissipated power P diss The peak channel temperature of the GaN HEMT RF device changes as a function of time.

[0052] In this embodiment, it can be considered that the response of the channel leakage current of the GaN HEMT device to the pulse excitation is complementary to the response of the channel temperature to the pulse excitation, and therefore has the same time constant. At this time, the transient response of the leakage current of the device under the pulse excitation can be expressed as:

[0053]

[0054] Where I(t) is the leakage current of the GaN HEMT RF device, I 0 is the leakage current of the GaN HEMT RF device when it reaches steady state under pulse bias voltage conditions, A i is the i-th order transient current response coefficient. By fitting the transient pulse current response of the device, the i-th order transient current response coefficient A can be obtained. i and the time constant τ of the i-th first-order RC thermal subnetwork i The fitting results are as follows Figure 8 shown.

[0055] Under the condition of fixed bias conditions, the leakage current of the GaN HEMT RF device is approximately linearly related to the channel peak temperature, and the transient current response coefficients of each order obtained by fitting are proportional to the thermal resistance of each order:

[0056]

[0057] According to the description of the third-order RC thermal subnetwork in Foster form and the fact that the transient current response coefficient of each order is proportional to the thermal resistance of each order (i.e., by combining the above equations (1), (2), (3) and (5)), the thermal resistance and thermal capacitance of each order of the third-order RC thermal subnetwork can be fitted. The transient thermal response of the device calculated by equation (4) is as follows: Fig. 9 shown.

[0058] Since the rate of change of the device thermal capacitance with temperature is very small, it can be considered as a constant. In this embodiment, the total thermal resistance of the device can be recalculated by formula (1) under different bias conditions, and the total thermal resistance can be redistributed by formula (5), and the time constants of each order thermal sub-network are calculated. The transient current response of the GaN HEMT RF device obtained by actual measurement and fitting is compared, as shown in FIG. Fig.10 shown.

[0059] This embodiment combines transient pulse current response, three-dimensional finite element thermal simulation and infrared thermal imaging test. The proposed transient thermal model takes into account the ambient temperature and dissipated power dependence of the thermal resistance parameters in the thermal sub-network, and can more accurately simulate the dynamic thermal characteristics of the device under actual working conditions. In addition, this embodiment uses transient pulse current response instead of complex, expensive and time-consuming optical methods to extract the values ​​of various order parameters of the thermal sub-network, thereby improving the efficiency of characterizing the transient thermal characteristics of GaN HEMT.

Claims

1. A method for characterizing the dynamic thermal characteristics of a GaN HEMT radio frequency device, characterized in that: The following steps are involved: S1, obtaining the structural parameters of the GaN HEMT RF device; S2, establishing a three-dimensional finite element thermal model according to the structural parameters of the GaN HEMT radio frequency device; S3, adjusting the material parameters of the three-dimensional finite element thermal model according to the infrared thermal imaging test results of the GaN HEMT radio frequency device; S4, based on the three-dimensional finite element thermal model, simulation is performed under different ambient temperatures and dissipated powers to obtain the thermal resistance of the GaN HEMT radio frequency device, and obtain the relationship between the thermal resistance and the ambient temperature and the dissipated power; S5, based on the relationship between thermal resistance, ambient temperature and dissipated power and combined with the transient pulse current response of the GaN HEMT radio frequency device, a third-order RC thermal sub-network model of the GaN HEMT radio frequency device in Foster form is established.

2. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 1, characterized in that: In the step S1, the structural parameters of the GaN HEMT radio frequency device are obtained by using a transmission electron microscope and an optical microscope.

3. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 1, characterized in that: The step S2 also includes: setting the thermal conductivity and interface thermal resistance of the material.

4. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 1, characterized in that: The step S3 specifically comprises: performing Gaussian filtering on the surface temperature distribution of the three-dimensional finite element thermal model according to the spatial resolution of infrared thermal imaging, comparing the filtered result with the infrared thermal imaging test result of the GaN HEMT radio frequency device, and adjusting the material parameters of the three-dimensional finite element thermal model until the filtered result fits the infrared thermal imaging test result of the GaN HEMT radio frequency device.

5. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 1, characterized in that: The relationship between the thermal resistance, the ambient temperature and the dissipated power in step S4 is expressed as: th =aT base +bP diss +c, where R th is the thermal resistance, T base is the ambient temperature, P diss is the dissipated power, and a, b, c are coefficients.

6. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 1, characterized in that: The step S5 specifically includes: According to the change of the isothermal line shape, the GaN HEMT radio frequency device is divided into three regions from top to bottom, wherein each region corresponds to a first-order RC thermal sub-network; A third-order RC thermal subnetwork in Foster form is used to describe the transient thermal characteristics of the GaN HEMT RF device; Under the condition of fixed bias conditions, the leakage current of the GaN HEMT radio frequency device is approximately linearly related to the channel peak temperature, and the transient current response coefficients of each order obtained by fitting are proportional to the thermal resistance of each order; According to the Foster form of the third-order RC thermal subnetwork description and the transient current response coefficient of each order is proportional to the thermal resistance of each order, the thermal resistance and thermal capacity of each order of the third-order RC thermal subnetwork are fitted.

7. The method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device according to claim 6, characterized in that: The third-order RC thermal subnetwork adopting the Foster form satisfies the following relationship: Among them, τ i is the time constant of the ith first-order RC thermal subnetwork, R i is the thermal resistance of the i-th first-order RC thermal subnetwork, T(t) is the dissipated power P diss The peak temperature of the GaN HEMT RF device channel changes with time as a function of the time. T base is the ambient temperature.

8. The method for characterizing dynamic thermal characteristics of GaN HEMT radio frequency devices according to claim 6, characterized in that: The transient response of the leakage current of the GaN HEMT RF device under pulse excitation is expressed as: Where I(t) is the leakage current of the GaN HEMT RF device, I0 is the leakage current of the GaN HEMT RF device when it reaches a steady state under the pulse bias voltage condition, and A i is the i-th order transient current response coefficient, τ i is the time constant of the i-th first-order RC thermal subnetwork.

9. The method for characterizing dynamic thermal characteristics of GaN HEMT radio frequency devices according to claim 6, characterized in that: Also includes: The total thermal resistance of the GaNHEMT RF device is recalculated under different bias conditions, and the total thermal resistance is redistributed through the relationship that the transient current response coefficient of each order is proportional to the thermal resistance of each order. The time constant of each order thermal sub-network is calculated, and the transient current response of the GaNHEMT RF device obtained by measurement and fitting is compared.

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