Potential-Adjusted Theory And New Structures Of High Speed Lateral IGBT

Widely used in all kinds of power electronics systems, IGBT(Insulated GateBipolar Transistor), which has some advantages, such as low driving power dissipation,high current holding capability, good thermal stability, high breakdown voltage andlarge SOA (Safe Operating Area), and which can be fabricated as discrete device or beintegrated to silicon-based and SOI-based (Silicon-On-Insulator-based) power IC(Integrated Circuit), is a typical structure of the new semiconductor power devices withconductivity modulation effect characteristics. The conductivity modulation effectpermits IGBT to have a low on-state voltage drop (von), but due to the removal of storedelectron-hole plasma in drift region, which is strongly dependent on the recombinationprocess of electron-hole pairs during turn-off period, it cause the turn-off time (toff)longer than that of MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor),which conducts by majority carrier during on and turn-off states. Long turn-off time,which limits the working frequency and make large turn-off power dissipation, is thebiggest barrier for further applications of IGBT. Finding new theory and new method ofaccelerating turn-off speed, improving the constraint relation of vonand toffis the basicquestion needing better solving.In this thesis, aiming at the basic constraint relation, with high speed Lateral IGBTon SOI substrate (SOI LIGBT) as the object of study, adopting the associative methodsof potential-adjusted analysis of the turn point from unipolar mode to bipolar mode,numerical simulation and experimentation, the new theory and the new device structuresare researched. A new theory, named Potential-Adjusted (PA) theory of high speedLateral IGBT, is proposed. Based on PA technology, two kinds of novel devices (highspeed LIGBTs with potential adjusting and3-D potential adjusting) are reported. Maininnovations of the research include:1. Potential-Adjusted (PA) theory of high speed Lateral IGBT is proposed. Theconcept of PA region, created by PA technology, is used to adjust the potentialdistribution of built-in reverse diode structure during on state, and to form an effective extracting path for excess carriers during turn-off state, which improves the electriccharacteristics of on state and turn-off state. This permits the device havenon-oscillation turning-on characteristics, high current holding capability,and highturn-off speed. For the PA technology and the new devices, to improve the constraintrelation of vonand toff, increasing the potential difference of the part located in anoderegion of the reverse diode structure is the common method to reduce the anode voltage(V_sb) of turn point from unipolar mode to bipolar mode, which eliminates snapbackphenomenon in I-V characteristics and increases conducting current during on state, andto form an effective extracting path for excess carriers, which accelerates the turn-offspeed during turn-off state. The expression of V_sb=(1+K·r)V0(IEEE Electron DeviceLetters, May,2010), providing the relation of anode voltage of turn point (Vsb) and holeinjecting voltage (V₀,0.7V for silicon), gives the way to design new high speed LIGBTbased on PA technology, which is reducing the potential adjusting factor (r) or3-Dadjusting factor (K). Eliminating snapback phenomenon and handling high current, atypical new structure, named NPN-NCA-LIGBT, make the anode voltage of turn pointfall to about Vsb=1.1V; and the ratios of turn-off times for the NPN-NCA-LIGBTcomparing to that of SA-NPN-LIGBT and conventional LIGBT are1:1.57and1:35.58,respectively.2. Based on PA technology, high speed LIGBTs with potential adjusting are firstlypresented. Increasing the potential difference of PA region is used to reduce the potentialadjusting factor (r), these novel structures include:(1) high speed LIGBT withnormalized PA region anode (NCA-LIGBT), it shows the prominent effect of thecreative concept of PA region in designing high speed LIGBT, but its high currentholding capability is sacrificed somewhat;(2) high speed LIGBTs with improved PAregion anode, including LIGBT with trench PA region anode (TNCA-LIGBT), LIGBTwith buried PA region anode (BNCA-LIGBT) and LIGBT with separated PA regionanode (SNCA-LIGBT), which are the improved structures of NCA-LIGBT;(3) highspeed LIGBT with enhanced PA region anode (ENCA-LIGBT), the forming of PAregion is used by isolative layer, and the device has both advantages of enhancedconductivity modulation effect and potential-adjusted electron extracting path;(4) highspeed LIGBT with depleted PA region anode (DNCA-LIGBT), the forming of PA regionis used by P-region of SOI wafer, and it is depleted during operation, the process flow is simplified and the capability of potential adjusting is enhanced.3. Based on PA technology, high speed LIGBTs with3-D potential adjusting arereported. The3-D design of potential adjusted extracting structure are used to reduceboth the potential adjusting factor (r) and3-D adjusting factor (K), these novelstructures include:(1) high speed LIGBT with segmented PA region anode(Seg-NCA-LIGBT), due to the concept of PA region and the3-D design of extractingstructure, it has the free selection between high current and high speed;(2) high speedLIGBT with dual extracting paths3-D PA region anode (NPN-NCA-LIGBT), due to theconcepts of PA region, NPN controlled and3-D design of extracting structure used foranode, it has two extracting paths for excess carriers during turn-off state, one is directconducting mode, and another is NPN reverse injecting mode;(3) high speed LIGBTswith split PA region anode, including LIGBT with normalized split PA region anode(Split-NCA-LIGBT) and LIGBT with striped split PA region anode(Split-Striped-NCA-LIGBT), split anode concept makes the anode split to independentbut coupled two parts, which eases up the constraint relation of on state and turn-offstate characteristics.The Potential-Adjusted (PA) theory of high speed Lateral IGBT and the newstructures are not only used for LIGBT on SOI substrates, but also used for othersemiconductor power devices with conductivity modulation effect characteristics, suchas silicon and other materials LIGBT, vertical IGBT, high speed diodes and so on.