A method for characterizing dynamic thermal characteristics of a GaN HEMT radio frequency device

Abstract

The application relates to a GaN HEMT radio frequency device dynamic thermal characteristic representation method, which comprises the following steps: acquiring structure parameters of a 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 infrared thermal imaging test results of the GaN HEMT radio frequency device; simulating under different environmental temperatures and dissipation powers based on the three-dimensional finite element thermal model, acquiring thermal resistance of the GaN HEMT radio frequency device, and obtaining the relationship between the thermal resistance and the environmental temperature and the dissipation power; and establishing a third-order RC thermal sub-network model in the form of Foster of the GaN HEMT radio frequency device based on the relationship between the thermal resistance and the environmental temperature and the dissipation power and in combination with a transient pulse current response of the GaN HEMT radio frequency device. The application can rapidly represent transient thermal characteristics of the device under different working conditions.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a method for characterizing the dynamic thermal properties of GaN HEMT radio frequency devices. Background Technology

[0002] Gallium nitride high electron mobility transistors (GaN HEMTs) are widely used in radio frequency (RF) and microwave fields such as power amplifiers, low-noise amplifiers, filters, and switches due to their superior performance. Compared to Si and GaAs devices, GaN has a larger bandgap, resulting in a higher breakdown voltage. Furthermore, due to the polarization effect, GaN HEMTs conduct electricity through a thin two-dimensional electron gas layer formed at the AlGaN / GaN heterojunction, leading to higher electron mobility and electron saturation velocity, making them one of the most advantageous semiconductor RF devices to date. However, because GaN HEMT devices typically operate at higher power densities and in high-frequency, high-power environments, significant internal self-heating leads to temperature increases and alters device performance. The degree of self-heating is usually reflected by thermal resistance, calculated using the following formula: Where ΔT is the device temperature rise, P diss Accurate steady-state thermal resistance extraction is crucial for the thermal management of GaN HEMT RF devices and the prediction of mean time to failure, as it is used to dissipate power. While steady-state thermal resistance extraction methods have been extensively studied, GaN HEMT RF devices actually operate under RF and pulse signals, thus requiring quantitative research on the dynamic thermal characteristics of GaN HEMT RF devices.

[0003] When a GaN HEMT RF device operates under a fixed DC bias for a period of time, it reaches a quasi-steady state internally. At this point, the device's thermal response is only related to its thermal resistance. However, when the device is under pulsed or continuous wave RF conditions, its thermal response changes over time. Current methods for extracting the transient thermal characteristics of these devices mainly include the temperature-sensitive electrical parameter method, reflectivity thermal imaging method, finite element transient thermal simulation method, and multi-order thermal network method.

[0004] Thermosensitive electrical parameter method can measure the transient thermal response of GaN HEMT RF devices by measuring electrical parameters such as on-resistance and gate Schottky contact resistance, which change approximately linearly with temperature. However, this method can only obtain the average temperature in the device channel, not the peak temperature, so the measured temperature is lower than the actual temperature. Reflectivity thermal imaging method uses the principle that the intensity of reflected light on the material surface changes with temperature to measure the temperature distribution on the device surface. This method can achieve submicron-level spatial resolution and nanosecond-level temporal resolution. However, the experimental equipment is expensive and the operation is complex. It ignores the change in reflectivity of the device surface caused by temperature changes and has a large measurement error when the device temperature is too high (e.g., above 200°C). Finite element transient thermal simulation method can simulate the transient thermal response of the device by setting parameters such as thermal conductivity, density, and constant pressure heat capacity of the device material. However, due to the uncertainty of the process, the material parameter setting has errors and cannot be measured. Furthermore, 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-level thermal network method is a commonly used method for characterizing the transient thermal response of GaN HEMT RF devices. By extracting the multi-level thermal network composed of the thermal resistance and thermal capacitance of the device, the transient thermal response of the device can be obtained quickly.

[0005] Currently, commonly used thermal resistance extraction methods are broadly classified into two categories: experimental extraction methods and simulation extraction methods. Experimental extraction methods include optical extraction, electrical extraction, and physical contact methods. Electrical extraction methods include comparative DC testing and pulse testing under different environments, as well as extraction of junction-shell thermal resistance using the structure function method. However, these methods can only obtain the average temperature within the device channel, and due to neglecting the self-heating effect under pulsed conditions, they may underestimate the device's thermal resistance to some extent. Physical contact methods can achieve nanometer-level thermal resistance measurement accuracy, but due to their complex operation, expensive equipment, and inability to determine the contact thermal resistance between the physical contact probe and the device, they have significant measurement uncertainties. Currently, the most commonly used thermal resistance measurement method remains optical measurement. While Raman spectroscopy and thermal reflectivity imaging offer high imaging accuracy, they cannot obtain the temperature distribution over a large area of ​​the device. Infrared thermal imaging is widely used in GaN HEMT device thermal resistance testing due to its ease of operation and ability to measure the surface heat distribution over a large area of ​​the device. However, it can only obtain the device surface temperature and has low spatial resolution, therefore 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 GaN HEMT RF devices, which can rapidly characterize the transient thermal characteristics of the devices under different operating conditions.

[0007] The technical solution adopted by this invention to solve its technical problem is: to provide a method for characterizing the dynamic thermal properties of GaN HEMT RF devices, comprising the following steps:

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

[0009] S2, Establish a three-dimensional finite element thermal model based on the structural parameters of the GaN HEMT RF device;

[0010] S3, Adjust the material parameters of the three-dimensional finite element thermal model based on the infrared thermal imaging test results of the GaN HEMT RF device;

[0011] S4. Based on the three-dimensional finite element thermal model, simulations are performed under different ambient temperatures and power dissipation to obtain the thermal resistance of the GaN HEMT RF device and the relationship between thermal resistance and ambient temperature and power dissipation.

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

[0013] In step S1, the structural parameters of the GaN HEMT RF device are obtained by transmission electron microscopy and optical microscopy.

[0014] Step S2 also includes setting the thermal conductivity and interfacial thermal resistance of the material.

[0015] Step S3 specifically involves: performing Gaussian filtering on the surface temperature distribution of the three-dimensional finite element thermal model based on the spatial resolution of infrared thermal imaging, 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.

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

[0017] Step S5 specifically includes:

[0018] Based on the change in the shape of the isotherm, the GaN HEMT RF device is divided into three regions from top to bottom, where each region corresponds to a first-order RC thermal network.

[0019] The transient thermal characteristics of the GaN HEMT RF device are described using a third-order RC thermal network of Foster form.

[0020] Under 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 are proportional to the thermal resistance of each order.

[0021] Based on the description of the third-order RC thermal network in Foster form and the fact that the transient current response coefficients of each order are proportional to the thermal resistance of each order, the thermal resistance and thermal capacity of each order of the third-order RC thermal network are obtained by fitting.

[0022] The third-order RC thermal network using the Foster form satisfies the following relationship: Where, τ i R is the time constant of the i-th first-order RC thermal network. i Let T(t) be the thermal resistance of the i-th first-order RC thermal network, and let P(t) be the power dissipation. diss The function of the change of the channel peak temperature of the GaNHEMT RF device over time, T base The ambient temperature.

[0023] The transient response of the leakage current of the GaN HEMT RF device under pulse excitation is expressed as follows: 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 steady state under pulse bias voltage conditions, and A i Let τ be the i-th order transient current response coefficient. i Let be the time constant of the i-th first-order RC thermal network.

[0024] The method for characterizing the dynamic thermal properties of GaN HEMT RF devices further includes: recalculating the total thermal resistance of the GaN HEMT RF device under different bias conditions, redistributing the total thermal resistance by means of the proportional relationship between the transient current response coefficients of each order and the thermal resistance of each order, calculating the time constants of each order thermal subnetwork, and comparing the measured and fitted transient current responses of the GaN HEMT RF device.

[0025] Beneficial effects

[0026] Due to the adoption of the above-mentioned technical solutions, this invention has the following advantages and positive effects compared with the prior art: This invention accurately obtains the device structure through focused ion beam, transmission electron microscopy and optical microscopy; it calibrates the three-dimensional finite element thermal simulation model of GaN HEMT device through infrared thermal imaging results, and obtains the thermal resistance value of the device related to power dissipation and ambient temperature from the calibrated model; based on the transient pulse current response of the device, a third-order RC thermal network model of GaN HEMT device in Foster form is established, which can quickly characterize the transient thermal characteristics of the device under different operating conditions. Attached Figure Description

[0027] Figure 1 This is a flowchart of the dynamic thermal characteristic characterization method for GaN HEMT radio frequency devices according to an embodiment of the present invention;

[0028] Figure 2 This is a flowchart of the infrared thermal imaging verification three-dimensional finite element thermal simulation in an embodiment of the present invention;

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

[0030] Figure 4 This is a comparison chart of simulation results and measured results under different ambient temperatures and power dissipation in the embodiments of the present invention;

[0031] Figure 5 This is a schematic diagram of the thermal resistance values ​​of the device obtained by simulation under different ambient temperatures and power dissipation in the embodiments of the present invention;

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

[0033] Figure 7 This is a topology diagram of a third-order Foster-type thermonic network in an embodiment of the present invention;

[0034] Figure 8 This is a graph showing the fitting results of transient pulse current in an embodiment of the present invention;

[0035] Figure 9 This is the transient thermal response diagram obtained by fitting the thermal network in an embodiment of the present invention;

[0036] Figure 10 This is a comparison chart of the transient current response obtained by actual measurement and fitting under different bias voltages in the embodiments of the present invention. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] The embodiments of the present invention relate to a method for characterizing the dynamic thermal properties of GaN HEMT radio frequency devices, such as... Figure 1 As shown, it includes the following steps:

[0039] Step S1: Obtain the structural parameters of the GaN HEMT RF device. In this step, transmission electron microscopy (TEM) and optical microscopy can be used to obtain the structural parameters of the GaN HEMT RF device.

[0040] Step S2: Establish a three-dimensional finite element thermal model based on the structural parameters of the GaN HEMT RF device; this step also includes setting parameters such as the thermal conductivity of the material and the interface thermal resistance.

[0041] Step S3: Adjust the material parameters of the three-dimensional finite element thermal model based on the infrared thermal imaging test results of the GaN HEMT RF device. Specifically, this step involves: applying a Gaussian filter to the surface temperature distribution of the three-dimensional finite element thermal model according to the spatial resolution of the infrared thermal imaging; comparing the filtered result with the infrared thermal imaging test results 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 results of the GaN HEMT RF device. The process is as follows: Figure 2 As shown, the fitting results are as follows: Figure 3 As shown. To verify the accuracy of the model, this step also requires comparing simulation and experimental results under different ambient temperatures and power dissipation conditions. The results are as follows. Figure 4 As shown.

[0042] Step S4: Based on the three-dimensional finite element thermal model, simulations are performed under different ambient temperatures and power dissipation to obtain the thermal resistance of the GaN HEMT RF device and the relationship between thermal resistance and ambient temperature and power dissipation. Figure 5 These are simulation results under different operating conditions. The final fitted expression for the relationship between thermal resistance and ambient temperature and power dissipation is as follows:

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

[0044] Among them, R th For thermal resistance, Tbase For ambient temperature, P diss This represents power dissipation.

[0045] Step S5: Based on the relationship between thermal resistance, ambient temperature, and power dissipation, and combined with the transient pulse current response of the GaN HEMT RF device, establish a third-order RC thermal network model of the GaN HEMT RF device in Foster form.

[0046] Because the area between the device channel region and the heat sink bottom surface contains multiple layers of material, such as Figure 6 As shown, the transient thermal response of a device cannot be accurately simulated using a first-order RC thermal network. Therefore, in this embodiment, the GaN HEMT RF device is first divided into three regions from top to bottom based on the change in isotherm shape: the GaN buffer layer plus interface thermal resistance region, the SiC substrate region, and the solder layer heat sink region. Each of these three regions corresponds to a first-order RC thermal network.

[0047] Although the parameters of the Cauer thermal network correspond to the actual structural layers of the device and have clear physical meanings, its mathematical calculation expressions are very complex, making it difficult to fit with measured data. Therefore, this embodiment uses a third-order RC thermal network of Foster form 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] Where, τ i R is the time constant of the i-th first-order RC thermal network. i Let T(t) be the thermal resistance of the i-th first-order RC thermal network, and let P(t) be the power dissipation. diss The function of the channel peak temperature of the GaNHEMT RF device as a function of time.

[0052] In this embodiment, the response of the channel leakage current of the GaN HEMT device to pulse excitation can be considered complementary to the response of the channel temperature to pulse excitation, and therefore have the same time constant. The transient response of the device's leakage current under pulse excitation can then be expressed as:

[0053]

[0054] 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 steady state under pulse bias voltage conditions, and A i Let be the i-th order transient current response coefficient. The i-th order transient current response coefficient A can be obtained by fitting the transient pulse current response of the device. i and the time constant τ of the i-th first-order RC thermal network i The fitting results are as follows Figure 8 As shown.

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

[0056]

[0057] Based on the description of the third-order RC thermal network in Foster form and the fact that the transient current response coefficients of each order are proportional to the thermal resistance of each order (i.e., by combining equations (1), (2), (3), and (5) above), the thermal resistance and thermal capacity of each order of the third-order RC thermal network can be obtained by fitting. The transient thermal response of the device calculated by equation (4) is as follows: Figure 9 As shown.

[0058] Since the rate of change of the device's thermal capacity with temperature is very small, it can be considered a constant. In this embodiment, the total thermal resistance of the device can be recalculated using equation (1) under different bias conditions, and the total thermal resistance can be redistributed using equation (5). The time constants of each order of thermal network are calculated, and the transient current response of the GaN HEMT RF device obtained by measurement and fitting is compared. Figure 10 As shown.

[0059] This embodiment combines transient pulse current response, three-dimensional finite element thermal simulation, and infrared thermal imaging testing. The proposed transient thermal model considers the environmental temperature and power dissipation dependence of thermal resistance parameters in the thermal subnetwork, enabling more accurate simulation of the dynamic thermal characteristics of the device under actual operating conditions. Furthermore, this embodiment uses transient pulse current response, rather than complex, expensive, and time-consuming optical methods, to extract the parameter values ​​of each order of the thermal subnetwork, improving the characterization efficiency of GaN HEMT transient thermal characteristics.

Claims

1. A method for characterizing the dynamic thermal properties of GaN HEMT RF devices, characterized in that, Includes the following steps: S1, Obtain the structural parameters of the GaN HEMT RF device; S2, Establish a three-dimensional finite element thermal model based on the structural parameters of the GaN HEMT RF device; S3, Adjust the material parameters of the three-dimensional finite element thermal model based on the infrared thermal imaging test results of the GaN HEMT RF device; S4. Based on the aforementioned three-dimensional finite element thermal model, simulations are performed under different ambient temperatures and power dissipation conditions to obtain the thermal resistance of the GaN HEMT RF device, and the relationship between thermal resistance and ambient temperature and power dissipation is obtained; wherein, the relationship between thermal resistance and ambient temperature and power dissipation is expressed as: R th =aT base +bP diss +c, where R th For thermal resistance, T base For ambient temperature, P diss Here, a, b, and c represent power dissipation, and a, b, and c are coefficients. S5. Based on the relationship between thermal resistance, ambient temperature, and power dissipation, and combined with the transient pulse current response of the GaN HEMT RF device, a third-order RC thermal network model of the GaN HEMT RF device in Foster form is established, specifically including: Based on the change in the shape of the isotherm, the GaN HEMT RF device is divided into three regions from top to bottom, where each region corresponds to a first-order RC thermal network. The transient thermal characteristics of the GaN HEMT RF device are described using a third-order RC thermal network in the form of a Foster. Under 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 are proportional to the thermal resistance of each order. Based on the description of the third-order RC thermal network in Foster form and the fact that the transient current response coefficients of each order are proportional to the thermal resistance of each order, the thermal resistance and thermal capacity of each order of the third-order RC thermal network are obtained by fitting.

2. The method for characterizing the dynamic thermal properties of GaN HEMT RF devices according to claim 1, characterized in that, In step S1, the structural parameters of the GaN HEMT RF device are obtained by transmission electron microscopy and optical microscopy.

3. The method for characterizing the dynamic thermal properties of GaN HEMT RF devices according to claim 1, characterized in that, Step S2 also includes setting the thermal conductivity and interfacial thermal resistance of the material.

4. The method for characterizing the dynamic thermal properties of GaN HEMT RF devices according to claim 1, characterized in that, Step S3 specifically involves: performing Gaussian filtering on the surface temperature distribution of the three-dimensional finite element thermal model based on the spatial resolution of infrared thermal imaging, 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.

5. The method for characterizing the dynamic thermal properties of GaN HEMT RF devices according to claim 1, characterized in that, The third-order RC thermal network using the Foster form satisfies the following relationship: Where, τ i R is the time constant of the i-th first-order RC thermal network. i Let T(t) be the thermal resistance of the i-th first-order RC thermal network, and let P(t) be the power dissipation. diss The function of the change of the channel peak temperature of the GaNHEMT RF device over time, T base The ambient temperature.

6. The method for characterizing the dynamic thermal properties of GaNHEMT RF devices according to claim 1, characterized in that, The transient response of the leakage current of the GaNHEMT RF device under pulse excitation is expressed as follows: 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 steady state under pulse bias voltage conditions, and A i Let τ be the transient current response coefficient of the i-th order. i Let be the time constant of the i-th first-order RC thermal network.

7. The method for characterizing the dynamic thermal properties of GaNHEMT RF devices according to claim 1, characterized in that, Also includes: The total thermal resistance of the GaNHEMT RF device was recalculated under different bias conditions. The total thermal resistance was redistributed based on the proportional relationship between the transient current response coefficients of each order and the thermal resistance of each order. The time constants of each order thermal subnetwork were calculated, and the transient current responses of the GaNHEMT RF device obtained by measurement and fitting were compared.

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