本文選題：AlGaN/GaN高電子遷移率晶體管 + 極化庫侖場散射　； 參考：《山東大學(xué)》2017年碩士論文

【摘要】：AlGaN/GaN高電子遷移率晶體管(AlGaN/GaN HEMTs)具有很多優(yōu)秀的性能特性,例如高擊穿場強、高輸出功率、高飽和電子漂移速度。此外,AlGaN/GaN異質(zhì)結(jié)材料的自發(fā)和壓電極化效應(yīng)使其在不摻雜的情況下,仍可產(chǎn)生密度高達1013cm-2的二維電子氣,因此在高頻、大功率集成電路中的應(yīng)用十分廣泛。隨著新器件結(jié)構(gòu)和新器件工藝的運用,AlGaN/GaN HEMTs器件性能越來越接近氮化鎵材料物理特性的極限。隨著對器件內(nèi)部等效電路研究逐漸深入,最近研究人員發(fā)現(xiàn)器件非本征參數(shù)寄生電阻嚴重影響器件的高頻性能和可靠性。其中器件在大信號下的截止振蕩頻率fT和非本征跨導(dǎo)gm,嚴重受制于寄生電阻,制約著器件在噪聲容限、開態(tài)電阻和傳輸延時時間等指標(biāo)上的進一步優(yōu)化。為了解寄生電阻的產(chǎn)生原因和作用機制,本文對溝道二維電子氣電子在溝道中輸運所受的主要散射作用進行討論,其中包括極化庫侖場(PCF)散射、極化光學(xué)聲子散射、界面粗糙度散射和壓電散射,并重點就PCF散射進行研究。PCF散射與柵源偏壓、源漏偏壓和柵面積均相關(guān),導(dǎo)致柵源和柵漏寄生電阻RS和RD也與柵源偏壓、源漏偏壓和柵面積相關(guān),從而對應(yīng)電流-電壓(I-V)輸出特性曲線的線性區(qū)和飽和區(qū)R和RD也不同。本論文分別研究了 AlGaN/GaN HEMTs器件線性區(qū)寄生電阻RS和飽和區(qū)寄生電阻RS與RD,研究了線性區(qū)RS與柵長和正向柵源偏壓的關(guān)聯(lián)關(guān)系,并研究得到了飽和區(qū)確定RS和RD的方法。我們制備出不同柵面積、不同柵源間距的AlGaN/GaN HEMTs,在不同外加?xùn)旁雌珘簵l件下測量出寄生電阻,并對器件溝道內(nèi)各種散射機制展開分析。最后,經(jīng)過散射理論模型計算的寄生電阻數(shù)值與實驗測試值的較好擬合證實了 PCF散射是Rs的重要影響因素,AlGaN/GaN HEMTs的寄生電阻與柵源偏壓、源漏偏壓和柵面積密切相關(guān)。具體包括以下內(nèi)容:1.極化庫侖場散射對器件線性區(qū)柵源溝道寄生電阻Rs的影響器件工藝之后,器件正常歐姆接觸退火工藝和柵極外加偏壓會改變AlGaN/GaN異質(zhì)界面處的極化電荷均勻分布狀態(tài),導(dǎo)致附加極化電荷的產(chǎn)生,引起PCF散射。經(jīng)TLM法測試,我們發(fā)現(xiàn)相同襯底上不同測試區(qū)域的器件歐姆接觸存在差異,表明同一片襯底上制作的歐姆接觸并不完全一致。歐姆接觸的質(zhì)量差異會干擾我們對器件在外加偏壓時柵下AlGaN勢壘層區(qū)域處由于逆壓電效應(yīng)產(chǎn)生的附加極化電荷的研究。為了減小歐姆接觸質(zhì)量差異的影響,我們設(shè)計了共用源極歐姆接觸的電子器件。由于同個臺面上的左右兩個柵極接觸共用同一個源極歐姆接觸,從而消除了不同歐姆接觸質(zhì)量差異的影響,由此可準確研究柵面積和柵源偏壓對RS的影響。在歐姆接觸下方區(qū)域,金屬原子擴散作用減弱了AlGaN勢壘層的壓電極化強度,并且歐姆接觸下方的附加極化電荷△σ1是一個與柵源偏壓無關(guān)的負值。在VGS0的情況下,柵下區(qū)域引入的隨柵源偏壓變化且為正值的△σ3和歐姆區(qū)域引入的不變且為負值的△σ1共同決定PCF散射勢。當(dāng)VGS增大,數(shù)值為正且增大的△σ3逐漸抵消數(shù)值為負且不變的Aσ1,最終Aσ3成為PCF散射勢的主導(dǎo)因素。對于同個樣品內(nèi)共用同一源極歐姆接觸的兩個AlGaN/GaN HEMTs器件,使用柵探針法測量RS時保持VGS在同一變化范圍以保證各器件中的柵下區(qū)域的△σ3相等。柵源間距相同,對于更大柵面積的器件柵下附加極化電荷總量更大,增強了 PCF散射勢的強度進而導(dǎo)致RS的增大。柵面積相同,器件柵下附加極化電荷總量相同,然而更大柵源間距的器件附加散射勢作用區(qū)域增大,降低了散射的強度,所以RS隨VGS變化幅度減小。最后,使用PCF散射理論模型,我們計算了各尺寸器件不同偏壓下的寄生電阻RS,并與器件寄生電阻的測試值進行對比,較好的擬合效果證實了用PCF散射理論解釋RS形成機制的合理性,也明確表明AlGaN/GaN HEMTs器件線性區(qū)RS與柵源偏壓和柵面積密切相關(guān)。2.極化庫侖場散射對長柵長器件飽和區(qū)寄生電阻的影響PCF散射是影響AlGaN/GaN HEMTs器件性能的重要散射機制。然而對于長柵長器件,對不同靜態(tài)偏置狀態(tài)下的飽和區(qū)寄生溝道電阻的研究并沒有考慮PCF散射的影響。由此,考慮PCF散射,并得到AlGaN/GaN HEMTs器件飽和區(qū)寄生電阻對提升器件特性至關(guān)重要。與深亞微米柵長器件不同,長柵長器件中源漏之間的電場不能使溝道載流子達到飽和漂移速度。因此,短柵長器件柵下的線性電勢分布并不適用于長柵長器件。長柵長器件的溝道電勢分布情況需要進一步研究。其一,在I-V輸出特性曲線中選取VGS=-3V-0V,VDS=8V的靜態(tài)偏置點,并使用改進的柵探針法測得器件的RS和RD。其二,根據(jù)寬禁帶半導(dǎo)體在制備肖特基柵極下的電荷控制模型,飽和區(qū)(VDS= 8V)時的柵下溝道電勢分布被分為兩個部分。緩變溝道近似溝道區(qū)域Ⅰ和夾斷溝道區(qū)域Ⅱ分別對應(yīng)柵下電勢從VC(0)變到Vknee和從Vknee變到VC(L)的區(qū)域。VC(0)和VC(L)分別是源、漏測柵極邊緣處的溝道電勢,Vknee近似認為是溝道恰好夾斷的溝道電勢。然后,使用PCF散射理論分析和確定AlGaN/GaN HEMTs器件溝道各處的附加極化電荷△σ的分布及其決定的附加散射勢。最后,綜合考慮極化光學(xué)聲子散射、界面粗糙度散射、壓電散射和極化庫侖場散射在內(nèi)的各種散射機制,模擬計算出不同偏置狀態(tài)下的RS和RD。理論計算結(jié)果和測試得到的RS和RD呈現(xiàn)較好的一致性,證明了理論計算的準確性。對于樣品3中的器件,歐姆接觸下方區(qū)域的附加極化電荷△σ1是一個與柵源偏壓無關(guān)的負值。各偏置狀態(tài)下的VGS為負值,因此柵下區(qū)域附加極化電荷△σ3為負值。取值為負值的△σ1和△σ3共同確定了 PCF附加散射勢。各測試點的柵源偏壓變化范圍是-3V到0V,逐漸減小的△σ3和固定不變的△σ1減弱了 PCF散射勢的強度,導(dǎo)致RS和RD的減小。另外,對于其他幾種散射機制,非柵極溝道區(qū)域內(nèi)電子溫度Te和二維電子氣密度n2D決定了它們的散射強度。由于樣品3中器件的電流較小不足以導(dǎo)致載流子明顯的熱聲子效應(yīng)和自熱效應(yīng)。常溫條件下,柵源和柵漏之間的溝道處的n2D在不同柵源偏壓VGS下為固定值。因此,各不同靜態(tài)偏置狀態(tài)下RS和RD的差異只能歸因于PCF散射勢的差異。這些研究結(jié)果證實由于PCF散射,AlGaN/GaN HEMTs器件寄生電阻RS和RD與柵源和源漏偏壓相關(guān);研究得到的確定AlGaN/GaN HEMTs器件飽和區(qū)寄生電阻RS和RD的方法是正確可行的方法。
[Abstract]:The AlGaN/GaN high electron mobility transistor (AlGaN/GaN HEMTs) has many excellent performance characteristics, such as high breakdown field strength, high output power and high saturation electron drift speed. In addition, the spontaneous and piezoelectric polarization effect of AlGaN/GaN heterojunction materials makes it still produce a two-dimensional electron gas with a density up to 1013cm-2 in the absence of doping. This is widely used in high frequency and high-power integrated circuits. With the application of new device structure and new device technology, the performance of AlGaN/GaN HEMTs devices is getting closer to the limit of physical properties of gallium nitride materials. With the study of the internal equivalent circuit of the device, the recent researchers found that the device is not the intrinsic parameter parasitic resistance. The high frequency performance and reliability of the device are seriously affected. The cut-off oscillation frequency fT and the non eigentransconductance GM under the large signal are seriously affected by the parasitic resistance, which restricts the further optimization of the device in the noise tolerance, open state resistance and transmission delay time. In order to solve the cause and mechanism of the generation resistance, this paper is concerned. The main scattering effects of the channel two-dimensional electron gas electron transport in the channel are discussed, including polarized Coulomb field (PCF) scattering, polarization optical phonon scattering, interface roughness scattering and piezoelectric scattering, and the study of PCF scattering is focused on.PCF scattering with gate source bias, source leakage bias and gate area, leading to gate source and grid. The leakage parasitic resistance RS and RD are also related to the gate bias voltage, the source leakage bias and the gate area, thus the linear region of the current voltage (I-V) output characteristic curve and the saturated zone R and RD are different. This paper studies the parasitic resistance RS and the parasitic resistance RS and RD of the linear region of the AlGaN/GaN HEMTs device, respectively, and studies the linear region RS and the gate length and the forward direction. The relationship between the bias voltage of the gate and the method of determining the RS and RD in the saturation area is studied. We have prepared the AlGaN/GaN HEMTs with different gate area and different gate spacing, and measured the parasitic resistance under the different bias voltage of the grid source, and analyzed the scattering mechanism in the channel. Finally, the scattering theory model was used to calculate the distribution. The good fitting of the value of the raw resistance and the test test confirmed that the PCF scattering is an important factor in the Rs. The parasitic resistance of the AlGaN/GaN HEMTs is closely related to the grid source bias, the source leakage bias and the gate area. The following contents are included: 1. the influence of the polarizing Coulomb scattering on the parasitic resistance Rs of the linear gate channel of the device, after the device process, The normal ohm contact annealing process and the grid applied bias will change the uniform distribution of polarization charge at the AlGaN/GaN heterointerface and lead to the generation of the additional polarized charge and cause the PCF scattering. By the TLM method, we find that the ohm contact of the devices on the same substrate is different, indicating that the same substrate is made on the same substrate. The ohm contact is not exactly the same. The mass difference of ohm contact interferes with the study of the additional polarization charge caused by the reverse piezoelectric effect at the AlGaN barrier layer under the applied bias voltage. In order to reduce the influence of the mass difference in ohmic contact, we designed the electronic devices that share the ohmic contact with the source. The influence of different ohm contact mass differences is eliminated by sharing the same source ohm contact with the left and right two grids on the same platform, which can accurately study the effect of gate area and gate bias on RS. In the area below ohm contact, the diffusion of metal atoms weakens the piezoelectric polarization of the AlGaN barrier layer. The additional polarized charge under the contact of the ohm is a negative value independent of the grid source bias. In the case of VGS0, the PCF scattering potential is determined by the variation of the grid source bias and the positive delta sigma 3 and the ohm region introduced in the lower gate region. When VGS increases, the value is positive and increasing delta sigma 3 gradually counteracts the number. The A sigma 1 is negative and constant, and the final A sigma 3 becomes the leading factor in the PCF scattering potential. For the two AlGaN/GaN HEMTs devices that share the same source ohm contact in the same sample, the VGS in the same range is kept in the same range by the gate probe method to ensure that the delta 3 in the sub gate area of the devices is equal. The gap between the gate source is the same, and the larger grid is for the larger grid. The total amount of additional polarized charge under the area of the device is greater, which increases the intensity of the PCF scattering potential and leads to the increase of the RS. The gate area is the same, the total amount of the additional polarized charge under the gate is the same. However, the additional scattering potential area of the device with larger gate spacing increases and the intensity of the scattering is reduced, so the amplitude of RS decreases with the VGS. Finally, the amplitude of the scattering is reduced. Using the PCF scattering theory model, we calculated the parasitic resistance RS under the different bias voltage of each size device, and compared with the test values of the parasitic resistance of the device. The better fitting results confirmed the rationality of the interpretation of the RS formation mechanism by the PCF scattering theory, and clearly indicated that the RS in the linear region of the AlGaN/GaN HEMTs device is biased with the gate source and the gate area density. The influence of.2. polarizing Coulomb scattering on the parasitic resistance of the long gate long device saturation region PCF scattering is an important scattering mechanism affecting the performance of AlGaN/GaN HEMTs devices. However, for long gate long devices, the study of the parasitic channel resistance in the saturated zone of different static bias States does not take into account the effect of PCF scattering. Thus, PCF dispersion is considered. It is important to shoot and obtain the parasitic resistance of the saturation region of the AlGaN/GaN HEMTs device. Unlike the deep sub micron gate long devices, the electric field between the source and leakage of the long gate long devices can not make the channel carrier reach the saturation drift velocity. Therefore, the linear potential distribution under the short gate grid is not suitable for long gate long devices. The distribution of channel potential in the long device needs further study. First, the VGS=-3V-0V, VDS=8V static bias point is selected in the I-V output characteristic curve, and the RS and RD. of the device are measured by the improved gate probe method. The charge control model under the wide band gap semiconductor under the Schottky gate and the saturation zone (VDS= 8V) is under the grid. The distribution of the channel potential is divided into two parts. The approximate channel region I and the clip channel region II correspond to the grid potential from VC (0) to Vknee and the region.VC (0) and VC (L) from Vknee to VC (L) respectively as the source, and the channel potential at the edge of the gate is missed, and Vknee approximately considers that the channel is exactly clipped trench potential. Then, so that The PCF scattering theory is used to analyze and determine the distribution of the additional polarization charge and the additional scattering potential of the additional polarized charge in the channel of the AlGaN/GaN HEMTs device. Finally, a variety of scattering mechanisms, such as polarization optical phonon scattering, interfacial roughness scattering, piezoelectric scattering and polarization Coulomb scattering, are considered. The theoretical calculation results of RS and RD. are in good agreement with the tested RS and RD, which proves the accuracy of the theoretical calculation. For the device in the sample 3, the additional polarized charge in the area below the ohm contact delta 1 is a negative value independent of the gate bias voltage. The VGS in each bias state is negative, so the polarizing electricity in the lower grid region is attached. The negative value of delta sigma 3 is negative. The negative value delta sigma 1 and delta 3 jointly determine the PCF additional scattering potential. The variation range of the gate source bias of each test point is -3V to 0V, the decreasing delta sigma 3 and the fixed delta sigma 1 weaken the intensity of the PCF scattering potential, resulting in the decrease of RS and RD. In addition, for several other scattering mechanisms, the non grid channel region The internal electron temperature Te and the two-dimensional electron gas density n2D determine their scattering intensity. Because the small current in the sample 3 is not enough to lead to the apparent thermal phonon effect and the self heat effect of the carrier. Under the normal temperature condition, the n2D between the gate and the gate leakage channel is fixed under the bias voltage of different gate sources. Therefore, the different static biasing. The difference between RS and RD can only be attributed to the difference of PCF scattering potential. These results confirm that due to PCF scattering, the parasitic resistance RS and RD of AlGaN/GaN HEMTs devices are related to the gate source and source leakage bias, and the method to determine the parasitic resistance RS and RD is a correct and feasible method to determine the saturation zone resistance of AlGaN/GaN HEMTs devices.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TN386

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