Multi-finger power SiGe HBTs for thermal stability enhancement over a wide biasing range

Multi-finger power SiGe heterojunction bipolar transistors (HBTs) with emitter ballasting resistor and non-uniform finger spacing are fabricated, and temperature profiles of them are measured. Experimental results show that both of them could improve the temperature profile compared with an HBT which has uniform finger spacing. For the HBT with emitter ballasting resistor, the ability to lower the peak temperature is weakened as power increases. However, for the HBT with non-uniform finger spacing, the ability to improve temperature profile is kept over a wide biasing range. Therefore, the experimental results directly prove that the technique of non-uniform finger spacing is a better method for enhancing the thermal stability of power HBTs over a wide biasing range.     

Thermal design studies of high-power heterojunction bipolartransistors

A theoretical thermoelectro-feedback model has been developed for the thermal design of high-power GaAlAs/GaAs heterojunction bipolar transistors (HBTs). The power-handling capability, thermal instability, junction temperature, and current distributions of HBTs with multiple emitter fingers have been numerically studied. The calculated results indicate that power HBTs on Si substrates (or with Si as the collector) have excellent potential power performance and reliability. The power-handling capability on Si is 3.5 and 2.7 times as large as that on GaAs and InP substrates, respectively. The peak junction temperature and temperature difference on the chip decrease in comparison to the commonly used Si homostructure power transistor with the same geometry and power dissipation. Thereby HBTs are promising for high-speed microwave and millimeter-wave applications. It has been also found that the nonuniform distribution of junction temperature and current can be greatly improved by a ballasting technique that uses unequal-valued emitter resistors     

500 mA AlGaAs/GaAs power heterojunction bipolar transistor

The current-voltage characteristics of 500 mA AlGaAs/GaAs power heterojunction bipolar transistors are reported and the influence of case temperature on current handling capability and current gain are analysed. Current handling capabilities of 400-800 mA/mm per emitter periphery at different case temperatures have been successfully demonstrated using a low-doped GaAs layer as an emitter ballasting resistor to obtain a uniform current distribution over individual emitter fingers. A current gain of 50 at a collector current of 500 mA was realised at room temperature for three elementary devices bonded in parallel, each device comprised ten (5*25 mu m/sup 2/) emitter fingers.<>     

Emitter-ballasting-resistor-free SiGe microwave powerheterojunction bipolar transistor

The emitter ballasting resistor is used to equalize the current distribution between the emitter stripes in power transistor, but it will degrade the output power, power gain, and power added efficiency. Experimental results indicate that the current gain of uniform-base SiGe heterojunction bipolar transistors (HBTs) decreases with the increase of the temperature above 160 K, so the current distribution is equalized by itself to some extent. Therefore, the microwave power SiGe HBTs without emitter ballasting resistor were fabricated for the first time, and the continuous output power of 5 W and power added efficiency of 63% were obtained under Class C operation at a frequency of 900 MHz. Hence, the emitter current density of the SiGe HBT's with emitter width of 6 μm is 0.79 A/cm     

发射极空气桥InGaP/GaAs HBT的DC和RF特性分析

为抑制电流增益崩塌,提高HBT的热稳定性,研制了发射极空气桥互连结构的HBT晶体管,应用ICCAP提取参数建立VBIC模型,结合模型参数对三种不同结构HBT的DC和RF特性进行比较分析.与引线爬坡互连结构相比,发射极空气桥互连结构HBT的热阻得到改善,热稳定性提高;与发射极电阻镇流方式相比,发射极空气桥HBT的截止频率(fT)相同,最大振荡频率(fmax)提高,最大稳定功率增益(MSG)高出约5dB.     

发射极镇流电阻对In_(0.49)Ga_(0 .51)P/GaAs HBT特性的影响

在发射极加一个镇流电阻可以解决在多个HBT并联时,常常出现电流坍塌的问题.研究了发射极镇流电阻对In0.49Ga0.51P/GaAs HBT直流及高频特性的影响,并对实验现象进行了理论分析.     

垂直发射极镇流电阻在HBT中的发射极电流集边效应中的作用

在异质结双极晶体管(HBT)功率器件中可以引入外延生长的发射极镇流电阻,以改善其热稳定性.通过理论计算和实验表明这种低掺杂的外延层不仅能作为镇流电阻,而且在功率HBT器件中还能非常有效地降低发射极电流集边效应.     

Technique for thermal stabilization of transistors

An alternative scheme to transistor thermal stabilization by emitter resistor ballasting is proposed. The technique involves a resistor with a negative temperature coefficient of resistance connected across the emitter-base junction which bypasses excess base current that tends to be drawn due to local transistor heating.     

微波功率SiGe HBT研究进展

Si的热导率比大部分化合物半导体(如GaAs)的热导率高,SiGe HBT在一个较宽的温度范围内稳定,SiGe HBT的发射结电压VBE的温度系数dVBE/dT比Si的小,双异质结SiGe HBT本身具有热-电耦合自调能力,所加镇流电阻可以较小,所有这些使SiGe HBT比GaAs HBT和SiBJT在功率处理能力上占一定优势。文章对微波功率SiGe HBT一些重要方面的国内外研究进展进行评述,希望对从事微波功率SiGe HBT的研究者有所帮助。     

Thermal performance of collector-up HBTs for small high-power amplifiers with a novel thermal via structure underneath the HBT fingers

We will describe the thermal performance of a special heterojunction bipolar transistor (HBT) structure for mobile communication systems, called a collector-up HBT. We calculated the thermal resistance between the HBT fingers and the bottom surface of a GaAs substrate using a finite element method (FEM). The results suggest that the thermal resistance of collector-up HBTs with thermal via structures can be reduced by 64% compared to the thermal resistance of ordinary emitter-up HBTs. They also show that the thickness of the InGaP emitter layer effects the thermal resistance of, and the temperature distribution in, the collector fingers of collector-up HBTs. Even though the thermal resistance of collector-up HBTs can be much smaller than that of emitter-up HBTs, a thermal interaction between the collector fingers still exists in multi-finger structures. We analyzed the temperature distribution in the collector fingers of a four-finger HBT structure and found that the thickness of the plated heat sink (PHS) was not sufficient to reduce the thermal interaction between the HBT fingers, and that optimization of the HBT location was needed to minimize the thermal interaction. We also found that the thickness of the InGaP emitter layer was the most important parameter for reducing thermal resistance, even in four-finger HBT structures. These calculation results can be used to reduce the temperature of collector-up HBTs and the temperature differences between the HBT fingers in the development of power amplifiers with collector-up HBTs.     

L波段150W宽带硅脉冲功率晶体管

设计了一种称之为多晶硅覆盖树技状结构的双极型微波功率晶体管。该器件采用掺砷多晶硅发射极，同时具备有覆盖和树枝状两种图形结构的优点。器件引入扩散电阻和分布式多晶硅电阻组合而成的发射极复合镇流电阻，实现对发射极电流二次镇流，器件表现出良好的微波性能和高的可靠性。经内匹配，在L波段脉冲输出大于100W（36V），脉宽150μs，工作比10％，增益大于7．5dB，效率大于45％，器件最大输出达150W（42V）。     

Self-aligned InGaP/GaAs heterojunction bipolar transistors formicrowave power application

As an alternative to AlGaAs/GaAs heterojunction bipolar transistors (HBTs) for microwave applications, InGaP/GaAs HBTs with carbon-doped base layers grown by metal organic molecular beam epitaxy (MOMBE) with excellent DC, RF, and microwave performance are demonstrated. As previously reported, with a 700-Å-thick base layer (135-Ω/sq sheet resistance), a DC current gain of 25, and cutoff frequency and maximum frequency of oscillation above 70 GHz were measured for a 2-μm×5-μm emitter area device. A device with 12 cells, each consisting of a 2-μm×15-μm emitter area device for a total emitter area of 360 μm², was power tested at 4 GHz under continuous-wave (CW) bias condition. The device delivered 0.6-W output power with 13-dB linear gain and a power-added efficiency of 50%     

A study of L-band GaAlAs/GaAs HBTs for high-voltage RF-power

The feasibility of GaAlAs/GaAs heterojunction bipolar transistors as power output transistors for 24–28V cellular base station applications was studied. A 1W, 25V test vehicle was fabricated, with predictable and uniform electrical parameters. Maximum output power was 1.02W with 9.1dB gain at 2GHz and 18V supply voltage. Characterization at more than 22V destroyed all devices, even if emitter ballasting resistors were used for thermal balance. Analysis indicated that the failures were caused by too wide emitters in combination with the high supply voltage, causing current crowding and large temperature spikes. Small (<2-3µm) horizontal emitter dimensions are required even with low base sheet resistivity, otherwise leading to destructive temperature non-uniformities, unless special arrangements to drastically reduce the thermal resistance can be applied.     

Thermal characterization of thermally-shunted heterojunctionbipolar transistors

Heterojunction Bipolar Transistors (HBTs) are potentially useful in a number of microwave applications, but they are severely limited by a current distribution instability caused by electrothermal interaction and the use of a low thermal conductivity substrate. A novel thermal management technique called “thermal shunting” has been developed to reduce thermal resistance and junction temperature non-uniformity. Thermal resistance measurements for thermally-shunted devices are presented. Specific thermal resistance measurements as low as 2.6×10^-4°C-cm²/W (147°C/W at 0.1 W for a device with a 177 μm² emitter area) have been obtained. Thermal resistance values obtained for thermally-shunted HBTs are substantially lower than those reported for conventional HBTs     

Determination of thermal resistance using Gummel measurement for InGaP/GaAs HBTs

In this paper, we propose a technique to determine thermal resistance of InGaP/GaAs heterojunction bipolar transistors (HBTs). The technique is based on Gummel measurement at only a few substrate temperatures. The major advantage of this technique is the simplicity in measurement, since the temperature-dependent parameter does not need to be determined for each device size. Therefore, when a number of devices need to be measured, this technique is less time-consuming. Another feature of this technique is the separation of the thermal resistance and emitter resistance, so that it is easier to optimize the emitter resistance. The result shown in this paper is measured from an InGaP/GaAs HBT, and is compared with another typical technique.     

SiGe HBT低频噪声PSPICE模拟分析

对SiGe HBT低频噪声的各噪声源进行了较全面的分析,据此建立了SPICE噪声等效电路模型,进一步用PSPICE软件对SiGe HBT的低频噪声特性进行了仿真模拟.研究了频率、基极电阻、工作电流和温度等因素对低频噪声的影响.模拟结果表明,相较于Si BJT和GaAs HBT,SiGe HBT具有更好的低频噪声特性;在低频范围内,可通过减小基极电阻、减小工作电流密度或减小发射极面积、降低器件的工作温度等措施来有效改善SiGe HBT的低频噪声特性.所得结果对SiGe HBT的设计和应用有重要意义.     

Structure optimization of multi-finger power SiGe HBTs for thermal stability improvement

The two-dimensional temperature profile of a power SiGe HBT with traditional uniform emitter finger spacing is calculated, which shows that there is a higher temperature in the central region of the device. With the aid of the theoretical analysis, an optimized structure of the HBT with non-uniform emitter finger spacing is presented. The peak temperature is lowered by 23.82 K, and the thermal resistance is also improved by 15.09% compared with that of the uniform one. The improvements above are ascribed to the increasing the spacing between fingers, and hence suppressing the heat flow from adjacent fingers to the center finger. Based on the analytical results, two types of HBTs with uniform emitter finger spacing and non-uniform emitter finger spacing are fabricated and their temperature profiles and thermal resistance are measured. The measured results agree well with the calculated results, verifying the accuracy of the calculations. For the HBT with non-uniform emitter finger spacing, the peak temperature and the thermal resistance are improved markedly over a wide biasing range compared with that of the uniform one. Therefore, both the calculated results and the experimental results verify that the optimized structure of power HBT with non-uniform emitter finger spacing is superior to the uniform emitter spacing structure for enhancing the thermal stability of power devices over a wide biasing range.     

微波大功率晶体管基极镇流方法研究

长期以来,解决微波功率晶体管的电流集中问题的通用做法是使用发射极镇流电阻．以及PTC,CTR热敏电阻等无源器件。区别于前者,本文提出一种实时有效的基极镇流解决方案,采用传感器探测结温,后续触发装置触发功率BJT基极发射极之间的镇流MOS管,来完成微波功率晶体管的过温保护,和常温解除功能,最终实现对功率器件的实时有效保护,使器件同时具备更高的可靠性,更优的电学性能。     

1 W Ku-band AlGaAs/GaAs power HBT's with 72% peak power-addedefficiency

High power and high-efficiency multi-finger heterojunction bipolar transistors (HBT's) have been successfully realized at Ku-band by using an optimum emitter ballasting resistor and a plated heat sink (PHS) structure. Output power of 1 W with power-added efficiency (PAE) of 72% at 12 GHz has been achieved from a 10-finger HBT with the total emitter size of 300 μm². 72% PAE with the output power density of 5.0 W/mm is the best performance ever reported for solid-state power devices with output powers more than 1 W at Ku-band