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58-553: BSIM (Berkeley Short-channel IGFET Model) refers to a family of MOSFET transistor models for integrated circuit design. It also refers to the BSIM group located in the Department of Electrical Engineering and Computer Sciences (EECS) at the University of California, Berkeley, that develops these models. Accurate transistor models are needed for electronic circuit simulation , which in turn

116-429: A depletion layer by forcing the positively charged holes away from the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, negatively charged acceptor ions (see doping ). If V G is high enough, a high concentration of negative charge carriers forms in an inversion layer located in a thin layer next to the interface between the semiconductor and the insulator. Conventionally,

174-551: A MOSFET. In the case of a p-type MOSFET, bulk inversion happens when the intrinsic energy level at the surface becomes smaller than the Fermi level at the surface. This can be seen on a band diagram. The Fermi level defines the type of semiconductor in discussion. If the Fermi level is equal to the Intrinsic level, the semiconductor is of intrinsic, or pure type. If the Fermi level lies closer to

232-535: A bipolar transistor. The subthreshold I–V curve depends exponentially upon threshold voltage, introducing a strong dependence on any manufacturing variation that affects threshold voltage; for example: variations in oxide thickness, junction depth, or body doping that change the degree of drain-induced barrier lowering. The resulting sensitivity to fabricational variations complicates optimization for leakage and performance. When V GS > V th and V DS < V GS  − V th : The transistor

290-404: A buried oxide is formed below a thin semiconductor layer. If the channel region between the gate dielectric and the buried oxide region is very thin, the channel is referred to as an ultrathin channel region with the source and drain regions formed on either side in or above the thin semiconductor layer. Other semiconductor materials may be employed. When the source and drain regions are formed above

348-476: A long-channel device, there is no drain voltage dependence of the current once V DS ≫ V T {\displaystyle V_{\text{DS}}\gg V_{\text{T}}} , but as channel length is reduced drain-induced barrier lowering introduces drain voltage dependence that depends in a complex way upon the device geometry (for example, the channel doping, the junction doping and so on). Frequently, threshold voltage V th for this mode

406-482: A new type of crystal-growth system that could produce single-crystal silicon boules , at that time a difficult prospect given silicon's high melting point. While work on the transistors continued, Shockley hit upon the idea of using a four-layer device (transistors are three) that would have the novel quality of locking into the "on" or "off" state with no further control inputs. Similar circuits required several transistors, typically three, so for large switching networks

464-509: A period of 20 years, 65 different companies were started by 1st or 2nd generation teams that traced their origins in Silicon Valley to Shockley Semiconductor. In 2014, Tech Crunch revisited Don Hoefler 's 1971 article , claiming 92 public companies of 130 descendant listed firms were then worth over US$ 2.1 Trillion. They also claimed over 2,000 companies could be traced back to Fairchild's eight co-founders. Shockley never managed to make

522-492: A recent Berkeley graduate. The Shockley Semiconductor Laboratory opened for business in a small commercial lot in nearby Mountain View in 1956. Initially he tried to hire more of his former workers from Bell Labs, but they were reticent to leave the east coast, then the center of most high-tech research. Instead, he assembled a team of young scientists and engineers, some from other parts of Bell Laboratories, and set about designing

580-466: A series of decisions that supported Shockley. Fed up, the group broke ranks and sought support from Fairchild Camera and Instrument , an Eastern U.S. company with considerable military contracts. In 1957, Fairchild Semiconductor was started with plans for making silicon transistors. Shockley called the young scientists the " traitorous eight " and said they would never be successful. The eight later left Fairchild and started companies of their own. Over

638-635: A set of model parameters may be used in different simulators, an industry working group was formed, the Compact Model Coalition , to choose, maintain, and promote the use of standard models. BSIM models, developed at UC Berkeley , are one of these standards. Other models supported by the council are PSP , HICUM , and MEXTRAM Archived 2014-12-28 at the Wayback Machine . The transistor models developed and currently maintained by UC Berkeley are: Original versions of BSIM models were written in

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696-480: A silicon MOS transistor in 1959 and successfully demonstrated a working MOS device with their Bell Labs team in 1960. Their team included E. E. LaBate and E. I. Povilonis who fabricated the device; M. O. Thurston, L. A. D’Asaro, and J. R. Ligenza who developed the diffusion processes, and H. K. Gummel and R. Lindner who characterized the device. This was a culmination of decades of field-effect research that began with Lilienfeld. The first MOS transistor at Bell Labs

754-507: A similar device in Europe. In the 1940s, Bell Labs scientists William Shockley , John Bardeen and Walter Houser Brattain attempted to build a field-effect device, which led to their discovery of the transistor effect. However, the structure failed to show the anticipated effects, due to the problem of surface states : traps on the semiconductor surface that hold electrons immobile. With no surface passivation , they were only able to build

812-401: A slighting when Bell promoted Bardeen and Brattain's names ahead of his own on the transistor's patent. However, others that worked with him suggested the reason for these issues was Shockley's abrasive management style, and it was this reason that he was constantly passed over for promotion within the company. These issues came to a head in 1953 and he took a sabbatical and returned to Caltech as

870-536: A superior product. Beckman agreed to back Shockley's efforts in this area, under the umbrella of his company, Beckman Instruments . However, Shockley's mother was aging and often ill, and he decided to live closer to her house in Palo Alto . Shockley set about recruiting his first four PhD physicists: William W. Happ who had previously worked on semiconductor devices at Raytheon , George Smoot Horsley and Leopoldo B. Valdes from Bell Labs, and Richard Victor Jones ,

928-424: A visiting professor. Shockley struck up a friendship with Arnold Orville Beckman , who had invented the pH meter in 1934. Shockley had become convinced that the natural capabilities of silicon meant it would eventually replace germanium as the primary material for transistor construction. Texas Instruments had recently started production of silicon transistors (in 1954), and Shockley thought he could create

986-748: Is a weak-inversion current, sometimes called subthreshold leakage. In weak inversion where the source is tied to bulk, the current varies exponentially with V GS {\displaystyle V_{\text{GS}}} as given approximately by: I D ≈ I D0 e V GS − V th n V T , {\displaystyle I_{\text{D}}\approx I_{\text{D0}}e^{\frac {V_{\text{GS}}-V_{\text{th}}}{nV_{\text{T}}}},} where I D0 {\displaystyle I_{\text{D0}}} = current at V GS = V th {\displaystyle V_{\text{GS}}=V_{\text{th}}} ,

1044-501: Is by far the most common transistor in digital circuits, as billions may be included in a memory chip or microprocessor. Since MOSFETs can be made with either p-type or n-type semiconductors, complementary pairs of MOS transistors can be used to make switching circuits with very low power consumption, in the form of CMOS logic . The basic principle of the field-effect transistor was first patented by Julius Edgar Lilienfeld in 1925. In 1934, inventor Oskar Heil independently patented

1102-709: Is defined as the gate voltage at which a selected value of current I D0 occurs, for example, I D0 = 1   μA, which may not be the same V th -value used in the equations for the following modes. Some micropower analog circuits are designed to take advantage of subthreshold conduction. By working in the weak-inversion region, the MOSFETs in these circuits deliver the highest possible transconductance-to-current ratio, namely: g m / I D = 1 / ( n V T ) {\displaystyle g_{m}/I_{\text{D}}=1/\left(nV_{\text{T}}\right)} , almost that of

1160-415: Is equivalent to a planar capacitor , with one of the electrodes replaced by a semiconductor. When a voltage is applied across a MOS structure, it modifies the distribution of charges in the semiconductor. If we consider a p-type semiconductor (with N A the density of acceptors , p the density of holes; p = N A in neutral bulk), a positive voltage, V G , from gate to body (see figure) creates

1218-401: Is needed for integrated circuit design . As the devices become smaller each process generation (see Moore's law ), new models are needed to accurately reflect the transistor's behavior. Commercial and industrial analog simulators (such as SPICE ) have added many other device models as technology advanced and earlier models became inaccurate. To attempt standardization of these models so that

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1276-501: Is the charge-carrier effective mobility, W {\displaystyle W} is the gate width, L {\displaystyle L} is the gate length and C ox {\displaystyle C_{\text{ox}}} is the gate oxide capacitance per unit area. The transition from the exponential subthreshold region to the triode region is not as sharp as the equations suggest. When V GS > V th and V DS ≥ (V GS  – V th ): The switch

1334-787: Is turned on, and a channel has been created which allows current between the drain and the source. The MOSFET operates like a resistor, controlled by the gate voltage relative to both the source and drain voltages. The current from drain to source is modeled as: I D = μ n C ox W L ( ( V GS − V t h ) V DS − V DS 2 2 ) {\displaystyle I_{\text{D}}=\mu _{n}C_{\text{ox}}{\frac {W}{L}}\left(\left(V_{\text{GS}}-V_{\rm {th}}\right)V_{\text{DS}}-{\frac {{V_{\text{DS}}}^{2}}{2}}\right)} where μ n {\displaystyle \mu _{n}}

1392-427: Is turned on, and a channel has been created, which allows current between the drain and source. Since the drain voltage is higher than the source voltage, the electrons spread out, and conduction is not through a narrow channel but through a broader, two- or three-dimensional current distribution extending away from the interface and deeper in the substrate. The onset of this region is also known as pinch-off to indicate

1450-447: The 45 nanometer node. When a voltage is applied between the gate and the source, the electric field generated penetrates through the oxide and creates an inversion layer or channel at the semiconductor-insulator interface. The inversion layer provides a channel through which current can pass between source and drain terminals. Varying the voltage between the gate and body modulates the conductivity of this layer and thereby controls

1508-478: The BJT and thyristor transistors. In 1955, Carl Frosch and Lincoln Derick accidentally grew a layer of silicon dioxide over the silicon wafer. By 1957, Frosch and Derick, using masking and predeposition, were able to manufacture planar transistors, in which drain and source were adjacent at the same surface. They showed that silicon dioxide insulated, protected silicon wafers and prevented dopants from diffusing into

1566-435: The C programming language . All newer versions of the models, except BSIM4 and BSIM3, support only Verilog-A . For example, the last version of BSIM-SOI which supported C was the version BSIM-SOIv4.4. IGFET The main advantage of a MOSFET is that it requires almost no input current to control the load current, when compared to bipolar junction transistors (BJTs). In an enhancement mode MOSFET, voltage applied to

1624-411: The 1930s and '40s he worked on electron devices , and increasingly with semiconductor materials, pioneering the field of solid state electronics. This led to the 1947 creation of the first transistor , in partnership with John Bardeen , Walter Brattain and others. Through the early 1950s a series of events led to Shockley becoming increasingly upset with Bell's management, and especially what he saw as

1682-432: The Fermi level and when the voltage reaches the threshold voltage, the intrinsic level does cross the Fermi level, and that is what is known as inversion. At that point, the surface of the semiconductor is inverted from p-type into n-type. If the Fermi level lies above the intrinsic level, the semiconductor is of n-type, therefore at inversion, when the intrinsic level reaches and crosses the Fermi level (which lies closer to

1740-459: The addition of n-type source and drain regions. The MOS capacitor structure is the heart of the MOSFET. Consider a MOS capacitor where the silicon base is of p-type. If a positive voltage is applied at the gate, holes which are at the surface of the p-type substrate will be repelled by the electric field generated by the voltage applied. At first, the holes will simply be repelled and what will remain on

1798-448: The body) are highly doped as signified by a "+" sign after the type of doping. If the MOSFET is an n-channel or nMOS FET, then the source and drain are n+ regions and the body is a p region. If the MOSFET is a p-channel or pMOS FET, then the source and drain are p+ regions and the body is a n region. The source is so named because it is the source of the charge carriers (electrons for n-channel, holes for p-channel) that flow through

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1856-406: The channel in whole or in part, they are referred to as raised source/drain regions. The operation of a MOSFET can be separated into three different modes, depending on the voltages at the terminals. In the following discussion, a simplified algebraic model is used. Modern MOSFET characteristics are more complex than the algebraic model presented here. For an enhancement-mode, n-channel MOSFET ,

1914-536: The channel-length modulation parameter, models current dependence on drain voltage due to the Early effect , or channel length modulation . According to this equation, a key design parameter, the MOSFET transconductance is: Shockley Semiconductor Laboratory Shockley Semiconductor Laboratory , later known as Shockley Transistor Corporation , was a pioneering semiconductor developer founded by William Shockley , and funded by Beckman Instruments , Inc., in 1955. It

1972-408: The channel; similarly, the drain is where the charge carriers leave the channel. The occupancy of the energy bands in a semiconductor is set by the position of the Fermi level relative to the semiconductor energy-band edges. With sufficient gate voltage, the valence band edge is driven far from the Fermi level, and holes from the body are driven away from the gate. At larger gate bias still, near

2030-747: The company. This was combined with Shockley's vacillating management of the projects; sometimes he felt that getting the basic transistors into immediate production was paramount, and would de-emphasize the Shockley diode project in order to make the "perfect" production system. This upset many of the employees, and mini-rebellions became commonplace. Eventually a group of the youngest employees – Julius Blank , Victor Grinich , Jean Hoerni , Eugene Kleiner , Jay Last , Gordon Moore , Robert Noyce , and Sheldon Roberts – went over Shockley's head to Arnold Beckman, demanding that Shockley be replaced. Beckman initially appeared to agree with their demands, but over time made

2088-414: The conduction band (valence band) then the semiconductor type will be of n-type (p-type). When the gate voltage is increased in a positive sense (for the given example), this will shift the intrinsic energy level band so that it will curve downwards towards the valence band. If the Fermi level lies closer to the valence band (for p-type), there will be a point when the Intrinsic level will start to cross

2146-422: The current flow between drain and source. This is known as enhancement mode. The traditional metal–oxide–semiconductor (MOS) structure is obtained by growing a layer of silicon dioxide ( SiO 2 ) on top of a silicon substrate, commonly by thermal oxidation and depositing a layer of metal or polycrystalline silicon (the latter is commonly used). As silicon dioxide is a dielectric material, its structure

2204-731: The depletion layer and C ox {\displaystyle C_{\text{ox}}} = capacitance of the oxide layer. This equation is generally used, but is only an adequate approximation for the source tied to the bulk. For the source not tied to the bulk, the subthreshold equation for drain current in saturation is I D ≈ I D0 e V G − V th n V T e − V S V T . {\displaystyle I_{\text{D}}\approx I_{\text{D0}}e^{\frac {V_{\text{G}}-V_{\text{th}}}{nV_{\text{T}}}}e^{-{\frac {V_{\text{S}}}{V_{\text{T}}}}}.} In

2262-464: The device may be referred to as a metal-insulator-semiconductor FET (MISFET). Compared to the MOS capacitor, the MOSFET includes two additional terminals ( source and drain ), each connected to individual highly doped regions that are separated by the body region. These regions can be either p or n type, but they must both be of the same type, and of opposite type to the body region. The source and drain (unlike

2320-468: The effect of thermal energy on the Fermi–Dirac distribution of electron energies which allow some of the more energetic electrons at the source to enter the channel and flow to the drain. This results in a subthreshold current that is an exponential function of gate-source voltage. While the current between drain and source should ideally be zero when the transistor is being used as a turned-off switch, there

2378-424: The electron is now fixed onto the atom and immobile. As the voltage at the gate increases, there will be a point at which the surface above the depletion region will be converted from p-type into n-type, as electrons from the bulk area will start to get attracted by the larger electric field. This is known as inversion . The threshold voltage at which this conversion happens is one of the most important parameters in

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2436-418: The four-layer diode a commercial success, in spite of eventually working out the technical details and entering production in the 1960s. The introduction of integrated circuits allowed the multiple transistors needed to produce a switch to be placed on a single "chip", thereby nullifying the parts-count advantage of Shockley's design. However, the company did have a number of other successful projects, including

2494-413: The gate leads to a higher electron density in the inversion layer and therefore increases the current flow between the source and drain. For gate voltages below the threshold value, the channel is lightly populated, and only a very small subthreshold leakage current can flow between the source and the drain. When a negative gate-source voltage (positive source-gate) is applied, it creates a p-channel at

2552-476: The gate terminal increases the conductivity of the device. In depletion mode transistors, voltage applied at the gate reduces the conductivity. The "metal" in the name MOSFET is sometimes a misnomer , because the gate material can be a layer of polysilicon (polycrystalline silicon). Similarly, "oxide" in the name can also be a misnomer, as different dielectric materials are used with the aim of obtaining strong channels with smaller applied voltages. The MOSFET

2610-408: The gate voltage at which the volume density of electrons in the inversion layer is the same as the volume density of holes in the body is called the threshold voltage . When the voltage between transistor gate and source ( V G ) exceeds the threshold voltage ( V th ), the difference is known as overdrive voltage . This structure with p-type body is the basis of the n-type MOSFET, which requires

2668-417: The increase in power consumption due to gate current leakage, a high-κ dielectric is used instead of silicon dioxide for the gate insulator, while polysilicon is replaced by metal gates (e.g. Intel , 2009). The gate is separated from the channel by a thin insulating layer, traditionally of silicon dioxide and later of silicon oxynitride . Some companies use a high-κ dielectric and metal gate combination in

2726-818: The lack of channel region near the drain. Although the channel does not extend the full length of the device, the electric field between the drain and the channel is very high, and conduction continues. The drain current is now weakly dependent upon drain voltage and controlled primarily by the gate-source voltage, and modeled approximately as: I D = μ n C ox 2 W L [ V GS − V th ] 2 [ 1 + λ V DS ] . {\displaystyle I_{\text{D}}={\frac {\mu _{n}C_{\text{ox}}}{2}}{\frac {W}{L}}\left[V_{\text{GS}}-V_{\text{th}}\right]^{2}\left[1+\lambda V_{\text{DS}}\right].} The additional factor involving λ,

2784-497: The new diodes would greatly reduce complexity. The four-layer diode is now called the Shockley diode . Shockley became convinced that the new device would be just as important as the transistor, and kept the entire project secret, even within the company. This led to increasingly paranoid behavior; in one famed incident he was convinced that a secretary's cut finger was a plot to injure him and ordered lie detector tests on everyone in

2842-399: The semiconductor surface the conduction band edge is brought close to the Fermi level, populating the surface with electrons in an inversion layer or n-channel at the interface between the p region and the oxide. This conducting channel extends between the source and the drain, and current is conducted through it when a voltage is applied between the two electrodes. Increasing the voltage on

2900-418: The surface of the n region, analogous to the n-channel case, but with opposite polarities of charges and voltages. When a voltage less negative than the threshold value (a negative voltage for the p-channel) is applied between gate and source, the channel disappears and only a very small subthreshold current can flow between the source and the drain. The device may comprise a silicon on insulator device in which

2958-410: The surface will be immobile (negative) atoms of the acceptor type, which creates a depletion region on the surface. A hole is created by an acceptor atom, e.g., boron, which has one less electron than a silicon atom. Holes are not actually repelled, being non-entities; electrons are attracted by the positive field, and fill these holes. This creates a depletion region where no charge carriers exist because

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3016-417: The thermal voltage V T = k T / q {\displaystyle V_{\text{T}}=kT/q} and the slope factor n is given by: n = 1 + C dep C ox , {\displaystyle n=1+{\frac {C_{\text{dep}}}{C_{\text{ox}}}},} with C dep {\displaystyle C_{\text{dep}}} = capacitance of

3074-443: The three operational modes are: When V GS < V th : where V GS {\displaystyle V_{\text{GS}}} is gate-to-source bias and V th {\displaystyle V_{\text{th}}} is the threshold voltage of the device. According to the basic threshold model, the transistor is turned off, and there is no conduction between drain and source. A more accurate model considers

3132-421: The valence band), the semiconductor type changes at the surface as dictated by the relative positions of the Fermi and Intrinsic energy levels. A MOSFET is based on the modulation of charge concentration by a MOS capacitance between a body electrode and a gate electrode located above the body and insulated from all other device regions by a gate dielectric layer. If dielectrics other than an oxide are employed,

3190-506: The wafer. Results of their work circulated around Bell Labs in the form of BTL memos before being published in 1957. At Shockley Semiconductor , Shockley had circulated the preprint of their article in December 1956 to his senior staff. J.R. Ligenza and W.G. Spitzer studied the mechanism of thermally grown oxides and fabricated a high quality Si/ SiO 2 stack in 1960. Following this research, Mohamed Atalla and Dawon Kahng proposed

3248-748: Was about 100 times slower than contemporary bipolar transistors and was initially seen as inferior. Nevertheless, Kahng pointed out several advantages of the device, notably ease of fabrication and its application in integrated circuits . Usually the semiconductor of choice is silicon . Some chip manufacturers, most notably IBM and Intel , use an alloy of silicon and germanium ( SiGe ) in MOSFET channels. Many semiconductors with better electrical properties than silicon, such as gallium arsenide , do not form good semiconductor-to-insulator interfaces, and thus are not suitable for MOSFETs. Research continues on creating insulators with acceptable electrical characteristics on other semiconductor materials. To overcome

3306-434: Was repurposed as a retail store. By 2015 plans were made to demolish the site to develop a new building complex. By 2017, the site was redeveloped with new signage marking it as the "Real Birthplace of Silicon Valley." William Shockley received his undergraduate degree from Caltech and moved east to complete his PhD at MIT with a focus on physics. He graduated in 1936 and immediately went to work at Bell Labs . Through

3364-440: Was the first high technology company in what came to be known as Silicon Valley to work on silicon-based semiconductor devices. In 1957, the eight leading scientists resigned and became the core of what became Fairchild Semiconductor . Shockley Semiconductor never recovered from this departure, and was purchased by Clevite in 1960, then sold to ITT in 1968, and shortly after, officially closed. The building remained, but

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