EECS130Integrated Circuit DevicesProfessor Ali Javey9/27/2007MS JunctionsLecture 1Reading: Chapter14Announcements• Reminder: Exam is next week!!!! It will cover semiconductor fundamentals, fabrication, pn diodes, and MS diodes.Announcements• Professor Javey will hold his OH at 3-5 pm for Wednesday of next week.• Course outline: we will finish covering MS junctions today and will start covering MOS/MOSFETs from Thursday. Sample Problems• Exercises within each chapter of your text• Review/supplement questions in your text• HW problems• Extra problems at the end of each chapter• Lecture examples/problems• Discussion section problemsMetal-Semiconductor ContactsTwo kinds of metal-semiconductor contacts:• metal on lightly doped silicon –rectifying Schottky diodes• metal on heavily doped silicon –low-resistance ohmic contactsχ: electron affinityFBFCs)( EE −+χ=ΦMetal Work FunctionThe work function of metals depend strongly on the “environment.”Workfunction, ΦMis an invariant property of metal. It is the minimum energy required to free up electrons from metal. Question: how can you change ΦS?Ideal MS ContactAssumptions:M and S are in intimate contact, on atomic scaleNo oxides or charges at the interfaceNo intermixing at the interfaceQuestion: how are Vbiand ΦBnrelated?Schottky Barrier Heights: Metal on SiφBntends to increase with increasing metal work functionSchottky Barrier Heights: metal silicide on SiSilicide-Si interfaces are more stable than metal-silicon interfaces. After metal is deposited on Si, an annealing step is applied to form a silicide-Si contact. The term metal-silicon contact includes silicide-Si contacts.Silicide ErSi1.7HfSi MoSi2ZrSi2TiSi2CoSi2WSi2NiSi2Pd2Si PtSiφBn (V) 0.28 0.45 0.55 0.55 0.61 0.65 0.67 0.67 0.75 0.87φBp (V) 0.55 0.49 0.45 0.45 0.43 0.43 0.35 0.23Does this depletion width equation look familiar? QuestionHow can you measure ΦBnand ΦBp?Using CV Data to Determine φBQuestion: How should we plot the CV data to extract φB?EvEvEcEfEfEcΦBnqVbiΦBnq(Vbi+ V)qVdepsdepWACε=Once Vbiis known, ΦΒcan be determined using:22)(21AqNVVCsdbiε+=dcBnfcBnbiNNkTEEqV ln)( −Φ=−−Φ=Using CV Data to Determine φBV1/C2−VbiIs the net current zero? Why?Question:How do p+n junctions differ from MS junctions under a forward bias?Question• How does the band diagram look for a MS junction with a Schottky barrier height of zero?Applications of Schottky Diodes• I0of a Schottky diode is 103to 108times larger than a PN junction diode, depending on φB . A larger I0means a smaller forward drop V. • A Schottky diode is the preferred rectifier in low voltage, high current applications.IVPN junctionSchottkyφBI VPN junctionSchottky diode
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